BLACK ROT, LEAF SPOT AND CANKER OF 
POMACEOUS FRUITS 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the Degree of 

DOCTOR OF PHILOSOPHY 



BY 

LEXEMUEL RAY HESLER 



Published as Cornell University Agricultural Experiment Stat. In 379, 

August 1916 



BLACK ROT, LEAF SPOT AND CANKER OF 
POMACEOUS FRUITS 



A THESIS 

Presented to the Faculty of the Graduate School 

of Cornell University for the Degree of 

DOCTOR OF PHILOSOPHY 



BY 

LEXEMUEL RAY HESLER 



Published as Cornell University Agricultural Experiment Station Bulletin 379 

August 1 91 6 



- 



S3731 

■ HI? 



i ct IBIS 



11 



CONTENTS 

PAGE 

ost considerations 53 

Plants concerned 53 

Varietal susceptibility 53 

Of fruit to black rot 53 

Of foliage to leaf spot 53 

Of limbs to canker 53 

The disease 54 

Names ... 54 

History 54 

The black rot of the fruit ■ • • 54 

The leaf spot ■ ■ • 55 

The canker form • • • 55 

Geographical occurrence ... 56 

Economic importance ... 58 

General considerations ... 5 s 

Nature of losses .... 58 

Injury to fruit 58 

Injury to foliage . 59 

Injury to lfmbs 59 

Symptoms 60 

On the fruit 60 

On the leaves 61 

On the limbs 62 

Other organs affect ed 63 

Etiology 64 

Morphology 64 

Peritheeia 64 

Pycnidia 66 

Pycnidial f< m xtx; 68 

Pycnospi ti , . . . 71 

Mycelium 74 

Sclerotia 75 

Chlamydosporc . 75 

Microconidia . 76 

Yeast forms. ...... 76 

Physiology 77 



Methods of isolation 77 

Cultural chai id I 77 

Cultural characters — specir.1... 77 

Protoplasmic streaming. . . 77 

Pathogenicity 78 

Black rot of apple. ... 78 

Leaf spot of apple-. ... 79 

Canker of apple 87 

Cross-inoculations and host relationships. . 95 

Names and synonymy 99 

Life history studies 101 

Source of the inoculum 101 

Method of spore discharge 103 

Time of spore discharge 104 

Agents of dissemination 10.5 

Infection courts 105 

Pycnospore germination 107 

Aseospore germination 1 08 

Incubation period 108 

51 



52 Contents 



PAGl 

Pathological histology 109 

Fruit 109 

Leaves 1 10 

Bark 1 1 1 

Control 1 1 ( 1 

Black rot .- 11 

Exclusion by legislation 116 

Spraying nu 

Handling of fruits 117 

Storage . 117 

Leaf spot.... 117 

Spraying 117 

Cultivation 1 1 ,s 

Canker 118 

Historical and introduce iry 118 

Surgical methods . . 1 1 < > 

Pruning . . . 119 

Removal of lira' is . 119 

Removal of diseased bark 120 

Wound treatment . 120 

Wound disinfection i:n 

Wound protection .120 

Wound healing '. ...123 

Wound cork . 123 

Wound wood 1 23 

Callus 123 

Spraying 1 -4 

General considerations . . . 124 

( irehard management 125 

Resistant varieties 125 

An enemy of the pathogenc 126 

Bibliography . . . , 1 21 > 



BLACK ROT, LEAF SPOT, AND CANKER OF POMACEOUS 

FRUITS' 

L. R. Hesler 
HOST CONSIDERATIONS 

PLANTS CONCERNED 

The black rot, leaf spot, and canker of pomaceous fruits is primarily 
a disease of the apple, Pyrus Malus L. It affects other trees also, however, 
especially the pear (Pyrus communis L.), the quince (Cydonia vulgaris 
Pers.), and the crab (Pyrus coronaria L.), showing on these hosts symp- 
toms similar to those on the apple. In addition the pathogene infests 
the dead parts of a great variety of other trees and shrubs, but in such 
cases there is usually no evidence that it has been the causal factor in the 
death of the tissues. In the State of New York, at least, this disease 
is of economic importance only on apple trees. 

VARIETAL SUSCEPTIBILITY 
OF FRUIT TO BLACK ROT 

The summer varieties of apples are affected by black rot at the time of 
ripening, while winter varieties commonly suffer in storage. In Con- 
necticut black rot is a most troublesome storage rot (Clinton, 1915: 5) , 2 

OF FOLIAGE TO LEAF SPOT 

Brooks and DeMeritt (1912:183), in New Hampshire, note striking 
differences in the varietal resistance of apple seedlings to leaf spot. In 
Virginia, Ben Davis and Black Twig are more severely attacked than are 
other varieties (Reed, Cooley, and Rogers, 1912:5). Salmon (1907), 
writing from England, states that among the varieties most affected 
there are Peasgood, Nonsuch, Cox's Orange, and others. The writer has 
noted that Chenango, Baldwin, Rhode Island, and Twenty Ounce show 
spotted foliage more commonly in New York than do other varieties. 

OF LIMBS TO CANKER 

Varieties of apples exhibit a marked difference in susceptibility to the 
disease, and this variation is not the same with respect to the different 
parts affected. In western New York Twenty Ounce is the variety most 
severely affected by the canker. This variety is rarely found unaffected 
by canker, even in orchards that are managed according to improved 
methods. Neglected trees of the Twenty Ounce variety are often killed. 

1 Also published as Cornell University Agricultural Experiment Station Bulletin .170 

2 Dates in parenthesis refer to bibliography, page 126. 

53 



54 Bulletin 379 

Paddock (1899 b: 181) says that certain growers in New York State 1 
noted that Twenty Ounce is most likely to be attacked. He lists other 
varieties in order of their susceptibility, as follows: Baldwin. Wagener, 
Rhode Island, Tompkins King. Regarding the Esopus, Paddock 
(1899b: 180) says that this variety has apparently run out because of I 
disease. In Ontario, Ben Davis, Northern Spy, and other vari< 
severely injured by the disease (McCready, 19 10). 

THE DISEASE 

NAMES 

The disease on the fruit is called black rot, ring rot. blossom-en 
and brown rot. The first name is descriptive and definite, and seems 
desirable. 

Lesions on the foliage are termed leaf spot, brown spot, and frog-> 
The names apple canker, black rot canker, and New York appl 
canker, are most commonly applied to the disease when it occurs on the 
bark. The term apple canker needs some qualification, since many kinds 
of cankers occur on the apple. It was under such an exigency that 
Paddock (1899b: 180, footnote) first used the name New York apple tree 
canker. The writer prefers to use this name regardless of its length, not 
alone because of priority, but also because of general usage. 

HISTORY 
THE BLACK ROT OF THE FRUIT 

The disease on the fruit was observed by Peck (1879:20) in Schoharie 
County, New York, and he quotes the remark of stagecoach passengers 
that they "never before knew of apples rotting on the tree." Arthur 
(1885) records black rot of quince fruit at Geneva, New York, and notes ■ 
the importance and infectious nature of the disease. Scribner (1890) 
notes the disease in New Jersey and describes the symptoms and causal 
nature. The same year Baccarini (1890), in Italy, observed the rotting 
of otherwise sound apples, pears, and peaches, the decay occurring in a 
storeroom of fruit gathered when ripe; this was a new appearance of the 
disease in that country. Two years later Halsted (1892) discussed the 
black rot of quince in New Jersey. Sturgis (1893, a and b) notes the 
disease on quinces in Connecticut in August, 1892, and later (1894) 
confirms the work of Halsted. Kinney (1895 c) figures and describes the 
disease in Rhode Island. In the same year it became an object of control 
measures in Kentucky (Garman, 1895). Black rot of apple is reported by 
Burrill and Blair (1901) in Illinois; they give a careful description of the 
disease and distinguish it from other apple rots. The following year 
Clinton (1902), writing from the same station, remarks that the disease on 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 55 

apples had attracted attention for several years, and that it was known 
to have occurred in Illinois at least as early as 1879. The disease as a 
storage rot was studied by Lamson (1902) in New Hampshire the same 
year. Faurot (19 12) describes the disease in Missouri. 

W. A.Orton (1904, 1905, 1906, 1907) publishes records of the black rot of 
pome fruits, the reports having come to him chiefly from the Middle West. 
In 1905 the black rot of quince and pear was especially injurious in Ohio. 
Evans (1910) called the attention of the apple growers of South Africa 
to the disease, which had just been found on apples at Grahamstown and 
also in a consignment of apples from Sidney, Australia. He urged the 
importance of excluding the disease from the Transvaal. Recent studies 
on black rot have been reported by Wolf (1913) in Alabama. 

THE LEAF SPOT 

The earliest record which the writer has found concerning the leaf spot 
is that by Alwood (1892), who reports brown spot of apple foliage in 
Virginia. He had noticed it for several years but states that it was not 
serious until 1891, when an outbreak occurred over the State. Kinney 
(1895 b) describes the disease in Rhode Island on apple and pear leaves, and 
says that it was very common in that State in 1895. Stewart (1896) 
reports having found the disease on Long Island in May, 1895; he notes 
that it had been observed in 1894 at Westbury, Long Island, by Professor 
Beach. Lamson (1899) lists the disease from New Hampshire and 
reports it as having done serious damage in some cases. Corbett (1900) 
reports " brown spot," or " frog-eye," as common throughout the southern 
and eastern counties of West Virginia, and as being more injurious than 
either blight or scab. Stewart and Eustace (1902) studied the cause and 
control of leaf spot in the eastern United States. The same year Clinton 
(1902) notes the severity of the disease in Illinois, and later (Clinton, 
1904) he reports its common occurrence in Connecticut. Stone and 
Smith (1903) record it as one of the most noticeable diseases of the season 
of 1902 in Massachusetts. Scott and Quaintance (1907) report the 
spotting of apple foliage in the Ozark region, and in the following year 
there appeared a more extensive work on the leaf spot problem by Scott 
and Rorer (1908). Work on the leaf spot was begun in New Hampshire 
in 1908 by I. M. Lewis (1908); this investigation was carried further by 
Brooks and DeMeritt (1912), who report it in full. Recent work on the 
leaf spot form of this disease has been published in Virginia by Crabill 
(1915)- 

THE CANKER FORM 

According to Paddock (1899 b: 180), orchardists have been familiar 
with this canker disease for years. Attention was first called to the 



56 Bulletin 379 

injury by Waite (1898 a), in a paper read at the meeting of the Western 
New York Horticultural Society in 1898. In the spring of 1898, Paddock 
(1898, a and b, and 1899 a) began investigations which extended through 
two seasons. He records having noticed the disease as early as 1891, 
and says that it became important about 1895. In 1897, according to 
Paddock (1899 b: 192), considerable "twig blight" was found at Odessa, 
New York. 

Mangin (1901) reports the disease in France on branches of apples, 
describing its symptoms in order, as he says, to put horticulturists on 
guard against invasion of the country by the pathogene. The same year 
Chester (1901, a and b), in Delaware, observed what he believed to be 
the same disease on apples and pears. His attention had been called to 
the canker on the latter host in the spring of 1900, near Smyrna. His 
illustrations suggest the possibility that the disease was the super- 
ficial bark canker of Edgerton (1908). A few years later Lochhead 
(1905) described the disease in Canada. Clinton (1907), writing from 
Connecticut, states that his attention was called to a peculiar disease 
of apple limbs in the spring of 1906. 

Another record of the disease which has appeared from France is that 
by Griffon and Maublanc (1910). They note very serious injury to 
pears in that country, and assert that at the national school of agriculture 
the disease was first known in 1908. A study of the disease was taken 
up in Canada by Bethune (1909). He reports a great amount of damage 
from cankers in the region east of Toronto. The following year a 
synopsis of the investigations in the province of Ontario was published 
by McCready (1910). A point of interest noted in this paper is that the 
great freeze of 1903-1904 in Prince Edward County marked the beginning 
of the canker epiphytotic there. The disease has received further attention 
in France by Arnaud (191 2), who lists it as occurring on a number of 
different plants. 

GEOGRAPHICAL OCCURRENCE 

The disease has a very general distribution throughout the temperate 
regions of the globe. Heretofore it has been regarded as a disease peculiar 
to eastern and middle western America, but it is now apparent that its 
limit is no longer to be so regarded. It has been found in Canada, par- 
ticularly in Ontario (Bethune, 1909), Quebec (Lochhead, 1905 and 1909), 
and Nova Scotia (Plant Pathology Herb., Cornell University Exsicc. 
no. 2657, and Giissow, letter to the writer). It occurs in Europe from 
Italy to England, according to the observations of Shear (1913:81-82). 
From England Berkeley (1836) reports it on apple fruit, while Salmon 
(1907) found it on apple foliage. It is unknown in Norway (Schoyen, 
letter to the writer), while both Ravn and Lind (letters) state that it 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 57 

is not present in Denmark. From Russia the disease has been reported 
by Potebnia (1907 and 1910). Jaczewsky (letter to the writer) states 
that the black rot and canker forms occur in the provinces of Kharkof 
and Tchernigof, and in the Transcaucasian and Turkestan regions. 
Potebnia (letter) has collected all the forms in Kursk, near the city of 
Fatej, and states it as his opinion that the disease occurs generally through- 
out Russia. Bubak (1909) reports it from Austria-Hungary. It probably 
occurs in Switzerland, Germany, and Holland, according to the general 
statement of Shear (igi3':82). Kirchner (1906:440) lists it from Germany. 
It may not be prevalent there, however, for Hollrung (letter) says the 
disease is not well known in Sachsen. Its occurrence in France is reported 
by Arnaud (1912) and others. The black rot form has been collected in the 
vicinity of Brussels, Belgium, by Bommer and Rousseau (1885). Some 
years ago it was introduced into Cape Colony from New South Wales 
(Evans, 1910:62, footnote). 

So far as the writer has been able to ascertain, the disease is widely 
distributed in America. It does not occur, however, so far as indicated 
by results from a circular letter sent to the plant pathologists of the state 
agricultural experiment stations, in the following States: Arizona, Colorado, 
Florida, Idaho, Louisiana, Montana, Nevada, North Dakota, South 
Dakota, Tennessee, Utah, Washington, Wyoming, and possibly Oregon. 
The canker form is commonest in the East, especially in New York, 
while fruit rot seems to occur more frequently in the New England and 
Middle Atlantic sections, although Wilson (1913) reports its occurrence 
throughout North America east of the Rocky Mountains. In the Middle 
Western States, particularly Ohio and Indiana, the pear and quince, 
as well as the apple, appear to have suffered considerably. Quaintance 
and Scott ( 1 9 1 2 ) state that the leaf spot occurs in all sections east of the 
Rocky Mountains where the apple is grown. In another publication 
Scott (1912) asserts that it is found in all humid sections of America. 
According to Reed, Cooley, and Rogers (1912:3-4), "frog-eye" is wide- 
spread in Virginia. Other States in which the disease occurs are Arkansas, 
Connecticut, Illinois, Maryland, Massachusetts, Missouri, Nebraska, New 
Hampshire, New York (particularly Long Island), Rhode Island, and 
West Virginia (Scott and Rorer, 1908:48-49). 

Probably no apple disease except apple scab is commoner in New York 
State than the one here considered. Throughout western New York 
the canker form is very prevalent. From replies to a circular letter sent 
to fruit growers in various parts of the State, it appears that this disease 
is more or less common and serious in all sections, except possibly in the 
central eastern part. The fruit and foliage rarely suffer appreciably in 
the State, although black rot and leaf spot are not infrequently found. 



58 Bulletin 379 

economic importance 
general considerations 

The nature of the losses caused by this disease makes very difficult 
the possibility of an estimate concerning them. So far as the writer has 
found, no reliable data are at hand in regard to this point. The com- 
bined injuries produced by the canker, the black rot, and the leaf spot 
are doubtless greater than is commonly supposed. It is undoubtedly true 
that the New York apple tree canker is often confused with other cankers 
by some growers, thus increasing the difficulty of obtaining reliable esti- 
mates on the destructiveness of this disease. 

It is generally considered that canker is one of the commonest and 
most troublesome diseases of the apple, although its destructiveness is 
not uniform in different parts of the country. According to Shear (1913 : 
81-82), the black rot disease of apple is found in Europe from Italy to 
England ; yet he states that noticeable injury from the disease in orchards 
has never been reported. On the other hand, Griffon and Maublanc 
(1910:308) state that in France the injury may be very serious. In 
contrast to the general situation in Europe, it may be noted that the 
damage done by this disease in America is great. 

NATURE OF LOSSES 

injury to fruit. Whenever pome fruits are attacked they are 
rendered worthless so far as their market value is concerned. The extent 
of injury may be small while the fruit still hangs on the tree, but ultimately 
in storage complete destruction is likely to result. Brooks (1909) states 
that in New Hampshire the black rot is very common and does con- 
siderable damage in cellar storage. Burrill and Blair (1901:2) report 
"great loss at times" in Illinois, and Clinton (1902), in the same State, 
compares the importance of bitter rot and black rot of apple. The latter 
he regards as likely to occur in every orchard to some extent. In Kentucky, 
black rot of apples is regarded as the commonest of fruit rots, according 
to Garman (1895:127). Stone (letter to the writer) estimates that 
in Massachusetts from eighty to ninety per cent of fruit rots is 
black rot. Evans (1910) reports a case in which rotting and mummified 
pome fruits appeared in a shipment to Cape Colony, and states in this 
regard : 

During the past three months four hundred and ninety-eight cases of apples and 
pears in this condition from Cape Colony have been detained, and in order to safe- 
guard the interests of Transvaal fruit growers, the Government, under Government 
Notice No. 569, of 18th June, 1908, have warned importers of fruit that all consignments 
of pomaceous fruits found infected with this fungus to the extent of one per cent and 
upwards will be destroyed upon arrival in this Colony or returned to the consignor. 

There is no reason to suppose that this number by any means represents the total 
amount of diseased fruit that has reached the Transvaal, to say nothing of the other 
parts of South Africa. 



Black Rot, Leaf Spot, and Canker of Pqmaceous Fruits 59 

injury to foliage. The damage to foliage depends on the extent of 
the infection. In the milder cases the injury is not appreciable. In the 
more severe cases, partial or even complete defoliation may occur from 
six weeks to two months before the ripening of the fruit, as a result of which 
the fruit either drops from the tree or remains small and is of poor quality. 
In such cases the fruit buds are so weakened as to decrease the possibility 
of a crop the following year, and the vitality of the trees is impaired. 
Alwood (1892:62) estimates a loss of seventy-five per cent of the foliage 
in a part of an old orchard in Virginia, while Stewart (1896) reports a 
case of complete defoliation of some trees on Long Island by the first of 
July. It is interesting to note, for comparison, that in 1900, in West 
Virginia, the disease was regarded by Corbett (1900) as more injurious to 
foliage than either blight or scab. Scott and Rorer (1909:10-11) have 
observed a case in which, as they believe, the pathogene causing this 
disease assisted in the killing, in late summer, of a large proportion of the 
fruit buds of the apple. The} 7 state that on Winesaps it would seem 
the pathogene alone is capable of killiiv ds. Further investigation 

is deemed desirable by these writers. 

injury to limbs. As a rule the canker is confined to the orchard, 
although Wilson (1913) says that young nursery stock may be killed. 
Bethune (1909:28-29) reports that cankers cause a great amount of 
damage in Ontario, Canada. J. W. Eastham (letter to the writer), of 
the Ontario Experiment Farm, states that this is the most prevalent 
canker in the region east of Toronto, and according to Brooks (1909) 
it is the commonest canker in New Hampshire. Warren and McCourt 
(1905:341) refer to this form of the disease as causing more loss in Wayne 
County, New York, than any other disease except scab. They report 
it as very serious in fourteen per cent of the orchards, and as doing con- 
siderable damage in nineteen per cent of them. In Niagara County, 
New York, Cummings (1909:304) found canker affecting the orchards as 
follows: slightly, sixty-one orchards; considerably, sixty-three; seriously, 
thirty-seven. Paddock (1899 b: 181, 188) cites a case in which, in an 
apple orchard of 80 acres, the trees on 30 acres were ruined and had been 
taken out; the trees on the remaining 50 acres were then of little value. 

In one apple orchard of three hundred and fifty trees under the writer's 
observation, a count made in August, 1913, showed about thirty-three 
per cent of the trees (Baldwin, Hubbardston, and Northern Spy varieties) 
with from one to three dead limbs each. On examination of the dead 
limbs the New York apple tree canker was found to be present on all. 
It was further observed that the pathogene causing the infection had lived 
over winter and had spread to such an extent that girdling had resulted 
and the foliage had turned yellow and wilted. The fruit on such limbs 



60 Bulletin 379 

soon shriveled and was lost. A careful count showed that approximately 
ten or twelve barrels of fruit were rendered worthless. The loss here 
might be placed at approximately twenty to twenty-five dollars, or about 
seven cents a tree. According to the United States Census for 19 10, 
there were in New York, on the 168,667 farms reporting, 11,248,203 apple 
trees of bearing age. 3 On this basis, assuming the losses in the above- 
mentioned orchard to be an average, the apparent annual loss would be 
about three-fourths of a million dollars for a single season in New York 
State. Many cases can be cited in which the infection by New York apple 
tree canker is very much more severe, while few orchards in the State, 
regardless of their careful management, are entirely free from the disease. 
Epiphytotics of this disease, such as have recently been experienced in 
the case of the chestnut blight, are of rare or unknown occurrence. It is 
characteristic of the disease to take a constant toll year after year, like the 
cereal smuts. To the losses so incurred must be added the cost of growing 
diseased limbs. In many cases these limbs die, resulting in the cost of their 
removal and destruction, which possibly does not seem great in a given 
year but is not negligible in the aggregate. 

SYMPTOMS 
ON THE FRUIT 

The disease on the fruit is primarily a ripe rot, but it may appear several 
weeks before maturity of the fruit. It may begin anywhere on the surface 
or at the blossom end. Frequently the lesions are centered about an 
injury such as that caused by insects or hail (Plate vn, 1). 

Usually there is only one spot on a fruit. The skin at first becomes 
brown in a small area, but later darkens, finally turning black. On green 
fruit the affected part may turn black before enlarging to any great extent, 
whereas on fruit that is ripe or ripening, the whole may be involved before 
it darkens appreciably. Often concentric bands of uniform breadth and 
of slightly different shades of color appear about the center of the lesion. 
The affected area is distinct from the healthy part, and the diseased tissues 
are not of unpleasant taste as in many fruit decays. Later stages in the 
development of the rot show a shriveled and much wrinkled surface, which 
typically becomes covered with black pustules (Plate vn, 2). These char- 
acters may be assumed within a month or in less time. Ultimately a dry 
mummy is produced, which may hang to the tree for a year or more. 

Black rot has been confused with brown rot and bitter rot, and even with 
soft rot. The brown rot disease produces a smooth, coal black, and shiny 
mummy, which is much less wrinkled than the black rot mummy. Bitter 
rot, in addition to its unpleasant taste, often shows pinkish specks in a 

» Bureau o£ the Census. Thirteenth Census of the United States taken in the year 1910, 7: 19s. 1913. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 6i 

localized region near the center of the lesion. The softening of the pulp 
in soft rot is not characteristic of black rot specimens. Perhaps the most 
distinctive characters of black rot are the long duration of the plumpness 
and juiciness of the tissues, and the occurrence of the above-mentioned 
black pustules. Under certain conditions the surface of the apple fruit 
also becomes studded with white tufts; but these are not commonly 
found and are not to be regarded as a diagnostic symptom. 

Fruits of the pear and the quince affected with black rot finally become 
dry and hard. In storage the peach becomes waxy when affected with 
the disease, according to Baccarini (1890:67). 

ON THE LEAVES 

The foliage of tne apple is more frequently attacked than that of the 
pear and the quince. The spots usually appear about the time the leaves 
open. Alwood (1892 : 62) notes this date as being about May 1 in Virginia. 
He records a second attack which becomes evident about June 20, and a 
third outbreak the last of July. Brooks and DeMeritt (1912:181) state 
that in New Hampshire apple leaf spot appears soon after the leaves 
unfold from the bud. In western New York spotting is more commonly 
apparent in July and August. The writer observed spots developed in 
September, 19 13, at Byron, New York. 

The number of lesions that may appear on a single leaf varies from one to 
several, and these may be scattered or localized on the surface (Plate vn, 3). 
The first evidence of a spot is a minute purple speck, which soon enlarges 
until it has reached a diameter of from two to ten millimeters, averaging 
about four millimeters. The purplish color is maintained for a con- 
siderable time, during which the margin is somewhat indefinite. Later the 
lesion is of a yellowish brown color and the spot assumes a more or less 
circular shape, while the margin becomes more definite. Still later the 
margin becomes elevated and the diseased area sunken. As the spots 
grow older they become lobed, due to a secondary extension of the patho- 
gene from one or more points, and finally a series of more or less concentric 
areas produces an irregular blotch in which the outline of the original 
spot can be recognized. The center has now become grayish brown, and 
the entire lesion presents an appearance which has given rise to the name 
frog-eye. 

The spots on the lower surface seem to enlarge as rapidly as those on 
the upper, but they are not so conspicuous. Sometimes the center of 
the spot on the lower surface is grayish brown. The whole diseased 
area may, however, merely appear dark and indefinite. 

Frequently small, black, dome-like bodies are found on the upper surface 
of the leaf, usually toward the center of the lesion. In severe cases the 



62 Bulletin 379 

leaves turn yellow and fall from the tree. According to Brooks and 
DeMeritt (1912:181), this leaf fall occurs from six to eight weeks earlier 
than would happen normally. Reed, Cooley, and Rogers (1912:3) 
maintain that defoliation may occur early enough for a new crop of 
leaves to be put forth the same season. Trees robbed of their foliage 
from year to year must eventually become greatly reduced in vitality 
and finally succumb to a premature death. 

Bordeaux injury is sometimes very similar to frog-eye leaf spot; Brooks 
and DeMeritt (1912:190) state that this is especially true if rains follow 
the application. Kinney (1895 b) notes also that injuries from the 
leaf miner (Tischeria malijoliella Clemens) are sometimes mistaken for 
leaf spot. 

ON THE LIMBS 

In western New York, young spots may be found on the bark at any 
time from the last of April until toward the close of the growing season. 
Numerous young cankers have been observed on Twenty Ounce trees 
in Monroe County orchards during the month of August. It is the 
rule that the larger limbs are much more susceptible than the twigs, 
and the trunks show comparatively few lesions. The cankers on the 
' trunks occur more or less uniformly on the southwest side of trees. The 
limbs more commonly show the diseased spots on the upper side. Lesions 
are very often found about the base of a small limb or about a wound 
in the bark. 

In the earlier stages of the formation of a canker, the bark is slightly 
sunken (Plates vin, and ix, 4) and reddish brown in color. The diseased 
area slowly increases in size and darkens, and, although not conspicuous 
at a distance, the spot is readily distinguished from healthy tissue on closer 
examination. Some lesions remain very small, measuring only a few centi- 
meters in their longer diameter; in such cases the canker usually dies 
out at the end of the year. Where the injury is larger, the diseased 
spot enlarges from year to year for a distance of a meter or even more. 

It is often observed that a canker is merely a superficial roughening 
of the bark. In other cases the bark is killed to the wood and becomes 
conspicuously cracked (Plate x). 

The discolored area may extend over a considerable surface; or, regard- 
less of its size, a crevice may appear at the margin, limiting, temporarily 
at least, the extent of the lesion. Further spread of the pathogene results 
in the formation of a prominent spot, which soon forms a second line 
of demarcation between the healthy and the diseased tissue. Repetition 
of this process from one or more points at the margin occurs, thus pro- 
ducing a lobed appearance (Plate xi, 2); or the spreading may arise from 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 63 

all points about the first marginal crack, so that a series of concentric 
crevices is developed, as described for frog-eye of the leaves. The 
bark remains closely appressed to the wood for at least a year; later 
the dead bark cracks and falls away, exposing the wood and a callus around 
the margin of the wound (Plate x, 3). 

Cankers that begin to form early in the season show numerous fruit- 
ing pustules of the pathogene scattered over the central area of the spot. 
These may not become evident, however, until the second season. 

Large limbs are rarely girdled the first year; the girdling comes about 
by the enlargement of the canker the following season. Complete encircling 
results in the death of the parts above the canker, as evidenced by the 
yellowing and droppingof the leaves (Plate xir, 1) and the shriveling of bark 
and fruit. It is not uncommon in such cases to find the fruit clinging 
to the twigs for a year or more. 

Clinton (1907) describes a peculiar type of lesion on apple limbs. He 
says, in part: 

Another and more peculiar feature of the trouble was the enlargement of the limbs 
into somewhat fusiform swellings, as shown in the illustration. In some cases several 
of the swellings followed one another on the same limb. These enlargements generally 
showed a greater swelling on one side than on the opposite, and often the bark was 
split down the more swollen side. Cross and longitudinal sections showed that the 
swellings were apparently the result of severe cold, which had injured the limbs unevenly 
along the branch, as shown by the blackened wood on the injured portion. 

Delacroix (1903a: 135) notes a thickening at the base of some cankers. 
This he finds to be a sort of cushion developed in a transverse direction 
in the healthy bark. The writer has occasionally observed cankers 
showing hypertrophy at the upper and lower ends of the diseased part 
(Plate x, 4). 

It is to be noted that on quince twigs the cankers are often very indefinite. 
A rare specimen is shown in Plate x, 5. The normal color of the bark 
is not distinctly lighter than that of the diseased part, so that on this 
host the disease doubtless passes unnoticed in many cases. 

other organs affected 

A unique case in Virginia of fall blossoming of the apple following 
the canker has been described by Reed (1908). This author found normal 
blossoms on an apple tree in the orchards of the Virginia Experiment 
Station on October 5. The cankers on the limbs had caused the death 
of more than half the top of the tree, and many branches, severely affected, 
had been able to make a very small amount of growth during the season. 
Reed says: " It was on such branches as these that fruit buds were found 
open on the above named date. Examination of the blossoms showed 
that they were normal as regards parts, color, and internal relationships. 



64 



Bulletin 379 



I am informed by Professor H. L. Price of the Department of Horticulture 
of this Experiment Station that this fall blossoming is not uncommon 
on trees which are badly affected by the black rot fungus." 

ETIOLOGY 

The pathogene here concerned is the fungus Physalospora Cydoniae 
Arnaud. 

MORPHOLOGY 

perithecia. The perithecia have been found by the writer on the 
twigs of apple (Pyrus mains L.) and of witch-hazel (Hamamelis 
virginiana L.), and have been described by him in another publication 




FlG. 18. PERITHECIUM OF PHYSALOSPORA CYDONIAE 

Camera lucida drawing of a median longisection ot a typical penthecium 

(Hesler, 1913:293). Recently the writer has found the ascogenous form 
on twigs of white oak {Quercns alba L.). 

The perithecia are usually scattered, standing separate from one another. 
Sometimes, however, from two to four fruit bodies are joined together, 
but no stroma has ever been observed. They are buried in the cortical 
tissues, protruding at maturity by a short, papillate ostiole. Their 
form is globose to subglobose, measuring from 180 to 324 /x in the vertical 
diameter by 300 to 400 u in the horizontal diameter, averaging about 
225 by 325 ft. 

A typical perithecium is shown in figure 18. The wall is differentiated 
into two layers. The thickness of the outer layer varies slightly with 
the sides and base of the perithecium, and the pseudo-cells are thick- 



Bulletin 379 



Plate VII 






SYMPTOMS OF THE DISEASE ON FRUIT AND FOLIAGE 

1. Types of infection on apples, early stages 

2. Apples reduced to mummies as a result of the disease 

3. Types of infection on apple leaves as commonly found in Ne%v York State 






3 s> 





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Bulletin 379 



. Plate IX 






-:**%** 




NATURAL CANKERS AND CANKERS PRODUCED BY ARTIFICIAL INOCULATION WITH 
rHYSALOSPORA CYDONIAE 

1. Natural infection on the left; artificial infection on the right. The latter inoculated on July I, 
[913, with a strain from Twenty Ounce apple bark. Photograph made September 30, 1913 

2. Canker on trunk of mature pear tree. Inoculation made July 18, 1910. photograph made 
September 1, 1911 

3. The result of inoculation by use of pyenospores from apple leaves. The healing process has 
occluded the wound before the pathogene could produce a large canker. Inoculation made July I, 
1912, photograph made September 20. 1913 

4. Canker on Baldwin twig produced artificially, using ascospores from apple. Inoculation made 
July 25, 1914, photograph made December 10, 1914 



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I 'LAVE XI 




INOCULATION EXPERIMENTS WITH PHYSALOSPORA CYDONIAE 

i. The three cankers uii the left produced by inoculating pear with ascospores from apple. 
Check on the right. Inoculations made June 6, 1913, photograph made September 20, 1913 

2. Canker on Twenty Ounce limb produced artificially, using pycnospores from apple. 
Inoculation made June 20, 1912, photograph made September 20, 1913 

3. Canker produced on pear by inoculation with ascospores from apple. The presence 
of pycnidia should be noted. Inoculation made June 6, 1913, photograph made September 
20, 1913 



Bulletin 379 



Plate XII 











/ 




NEW YORK APPLE TREE CANKER 

r. Twenty Ounce apple tree, some of the larger limbs of which have been girdled by the fungus. 
Evidence that this has occurred is found in the defoliated tops of affected limbs 

j. External view at left, and internal view at right, of young black rot lesions on apple; the specimen 
on the right shi iws the I issues invi >lved 



Bulletin 379 



Plate XIII 



\ 





VARIOUS STAGES OF PHYSALOSPORA CYDOXIAE 

1. Showing differences in growth on nutrient a^ar from pycnospores (heavy dark growth on left) 
and from asc ispores (scant growth on right) 

2. Photomicrograph of asci, ascospores, and paraphyses from a single perithecium 

3. Sclerotia as they appear in pure culture 

4. Twig of apple, showing dark masses of pycnospores which have oozed from the pycnidia when 
the twin was kept in a moist chamber 



Bulletin* 379 



Plate XIV 




INOCULATION EXPERIMENTS WITH PHYSALOSPORA CYDONI.E 

i. Canker on right, check on left. Inoculation made July i, 1912, using pycnospores 
from pear, the fungus having followed fire blight. Photograph made September 20, 19*3 

2. Comparison of two different apple strains on pear. Specimen shown on left inoculated 
with ascospores from apple. Specimen shown in center inoculated with pycnospores from 
apple, following fire blight. The very slight infection should be noted. Check on right. 
Inoculation made June 6, 1913. photograph made September 20, 1913 



Black Rot, Leaf vSpot, and Canker of Pomaceous Fruits 65 





Fig. 19. asci and 
paraphyses of 
physalospora 
cydoniae 

Camera lucida draw- 
ing of asci and paraph- 
yses, showing structure 
of the latter and typical 
arrangement of asco- 
spores in the ascus 



walled. The inner, thin-walled layer is of very uniform diameter. In 
cases in which the perithecium is depressed, the outer layer is reduced 
at the base and is from one to three pseudo-cells in 
thickness, whereas the lateral outer walls are from two 
to five layers of pseudo-cells in thickness. The ostiole 
appears as a narrow passage in the papilla, the walls 
of which show the same distinct layers as those just 
described for the sides and base of the perithecium. 

The asci, with the interspersed paraphyses, usually fill 
the cavity of the perithecium. Arnaud (1912 : 1 1) states 
that in general the paraphyses are formed by rows of 

cells which 
in the ma- 
ture peri- 
t h e c i u m 
are sepa- 
rated one 
from an- 
ot h e r in 
the form of 
distinct fil- 
aments. He says that in cer- 
tain cases, however, the 
paraphyses remain aggluti- 
nated by their walls and 
appear in section like rows of 
cellular cavities, as in Cucur- 
bitaria (C. Spartii and other 
species). He explains that if 
the rows of cells are not very 
numerous the existence of the 
paraphyses may become un- 
certain. Arnaud finds this 
the case with Physalospora 
Cydoniae. The writer, how- 
ever, has not observed this 
condition of the paraphyses; 
to him thev apoear distinct 

The upper series represents variations as found on apple 
bark. The lower series shows variations from bark of witch- and IlOn-Septate (Fig. io). 
hazel . ' 

The asci are abundant; 
asci crushed from one perithecium are shown in Plate xiii, 2. They are 
usually clavate, although they sometimes tend to be cylindrical, measuring 



Fig. 20. 



ASCI OF PHYSALOSPORA CYDONIAE FROM 
DIFFERENT HOSTS 



66 



Bulletin 379 






TYPES OF ASCOSPOUES 
SALOSPORA CYDONIAE 



from 21 to 32 ix b> 130 to 180 il. The tip of the ascus is thickened, but a 
complete canal from the inner wall to the outside has not been observed; 

only a suggestion of such a canal 
has been seen even after the peri- 
thecia had been kept in a moist 
chamber for several hours. Varia- 
tions of asci from different hosts are 
shown in figure 20. 

The ascospores are ellipsoidal, or 
often inequilateral (Fig. 21); they 
measure from 10.8 to 15.2 ix by 23.4 
to 34.2 yu, averaging 11.5 by 28//. 
They are hyaline to greenish yellow. 
Under ordinary conditions the spores 
show a very thin gelatinous sheath, 
but after they have been in a satu- 
rated atmosphere for a few hours the 
sheath becomes very broad and evi- 
dent. The arrangement of the spores 

A. Typical mature ascospores as found in nature; in the aSCUS IS more Or leSS blSenate. 
B. ascospores, showing stages in the development of rn.-i ««~~~'U r-^c o*-^ ^ic-f-i-,-, f n-n^ o*-c 

the gelatinous sheath; c. old ascospores, showing ->- ne parapnyses are distinct ana are 
peculiar contents occasionally branched near the tip. 

Not infrequently the apex shows a tendency to be clavate. 

The number of spores in each ascus is typically eight, but exceptions 
have been found in the fungus on apple twigs. The variation ranges from 
two to eight spores within an ascus, all intervening numbers having been 
observed. Four-spored asci are not uncommon (Fig. 20). The contents 
of ascospores are either densely granular, or vacuolate and oily. Two 
guttules are occasionally found. 

pycnidia. The morphology of the pycnidial form of this fungus is 
variable (Fig. 22). The pycnidia are situated in the cortical tissues 
and are usually scattered and distinct, although on the same organ of 
the host they may be single, confluent, or united into a stroma. The 
number of pycnidia per unit of area is usually less on woody substrata 
than on fruits; on apple fruit there may be from one hundred and twenty 
to one hundred and fifty pycnidia per square centimeter. 

The typical simple pycnidium (Fig. 22, a) measures from 200 to 300 fi 
in each diameter, whereas the compound fruit body may vary from 200 
to 460/* in the vertical diameter and from 200 to 720 yu in the horizontal 
diameter (Fig. 22, g) . Their shape is in general the same as that of the 
perithecia, globose to subglobose, and they have the same distinct outer 
and inner walls. The thickness of the entire pycnidial wall is variable, 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 67 



as in the case of the perithecium. The basal part is thinner in the case 
of the subglobose fruit bodies. This condition may be attributed to the 
fact that less protection is needed at the base; or perhaps here the thick- 
ness may be partially determined by mechanical pressure brought about 
by the resistance offered by the host tissue. 

Arising from the inner thin-walled cells are the pycnosporophores, which 




FlG. 22. VARIATIONS OF PYCNIDIA OF PHYSALOSPORA CYDONIAE 

A, Typical simple unilocular pycnidium; B, pycnidium with long neck, similar to C but with an ostiolum; 
C, pycnidium similar to B, ostiolum not yet developed; D, pycnidium from apple leaf; E, hair-like out- 
growths on the tip of an ostiolum, developed under moist conditions; F, pycnidium with mound-like struc- 
ture at base; G, pycnidium which approaches in appearance the fruiting body o: species belonging to the 
form-genus Botryodiplodia 

extend entad. They are clavate, flask-shaped, or cylindrical. They may 
be as long as the spore itself, from 25 to 30 yu, or may measure less than 
Sju; the average dimensions are from 10 to 1 5 ju by 3 to 4/1. At the tip 
of each is developed a pycnospore. 

In some cases there is a mound-like structure at the base of the pycnidium 
(Fig. 22, f). This is illustrated by Duggar( 1 909 1353, fig. 171). It has been 
a matter of conjecture whether this may appear only in an oblique tan- 



68 Bulletin 379 

gential section, or whether it is a bilocular tendency. It does not seem 
possible that any such structure would appear merely in a section that 
was not cut vertically. If this were true, the question would then arise 
as to whether this same appearance would not extend at all points along 
the lining of the cavity, and hence merely make the wall thicker rather 
than give it the aspect just described. It seems, therefore, to be a 
bilocular tendency. 

Frequently the pycnidium approaches and even reaches the condition 
characteristic of the form-genus Botryodiplodia (Fig. 22, g). The sporog- 
enous layer extends inward at places, giving the inner wall a corrugated 
appearance. This condition is found in nature and has been developed 
in culture from spores in pycnidia which originally did not show this 
structure. The simplest condition suggesting the form-genus Botryodi- 
plodia is found when a single mound-like structure occurs at the base of 
the pycnidium, as previously described (Fig. 22, f). Frequently this finds 
its expression in the form of a bilocular condition, which is a step nearer 
the Botryodiplodia type. 

The ostiolum offers some interesting variations. Miss Walker (1908) 
describes a form which she believes lacks an ostiolum. In the place of 
the typical conical ostiolate neck there was found a much-thickened wall 
at the apex of the fruiting body, and the papilla itself appeared longer 
than usual. The writer has cultured the ostiolate form from an apple, 
and has obtained, on various agars and on apple fruit, pycnidia having 
the characteristics described by Miss Walker (Fig. 22, c). The evidence at 
hand indicates that a pore may or may not be present, depending some- 
what on the time of year and on weather conditions. In any case an 
ostiolum will ultimately be developed (Fig. 22, a, b, d). Brooks and De 
Meritt (191c: 184) report three types of pycnidia but all forms are ostiolate. 
It does not seem likely that any strain will remain void of an ostiolum 
throughout its history. A strongly papillate form similar to that shewn 
in figure 22, c, but with an ostiole developed, is illustrated in figure 22, e. 
A form of the fungus which at first appeared to have a non-erumpent 
pycnidium was found in apple bark and twigs of Cclastrus scandens L. 
After the material had been in a moist chamber for a few days, however, 
the pycnidia broke through the epidermis. 

In conclusion it may be stated that the pycnidia may vary in mor- 
phology on different host plants, yet this variation is no greater than that 
on the same host plant. 

pycnidial formation. The pycnidia arise from the mycelium and are 
found abundantly on cankers and decayed fruit. Also they may be 
produced on various artificial media. They occur sparingly on spotted 
leaves. 



Black Rot, Leaf Spot, and Cankep of Pomaceous Fruits 6g 

So far as has been determined, the process of formation is similar on 
different substrata. The earlier stages are more accurately followed 
in agar cultures than on any organs of the host plant. The writer's obser- 
vations have been made by examining petri-dish cultures under the low 
power of the microscope and by the use of prepared slides from such 
cultures. The material was prepared as follows: Pycnospores or hyphal 
threads were planted in the center of agar plates, and, as the hyphae 
developed, pycnidia appeared in more or less definite concentric rings. 
In this way the oldest pycnidia were nearest the starting point, whereas 
the youngest were found near the margin of the culture, the stages between 




FlG. 23. DEVELOPMENTAL STAGES OF THE PYCNIDIUM 

A, Early stage in pycnidial development. The hyphas have become closely septate, are broadened, 
and are beginning to tangle. B, Early stage in the process, showing the origin of hypha? which enter 
into the pycnidium. Some come from adjacent hyphas, others arise from cells of the threads in the 
immediate tangle. C. Early stage. Branching of hypha, preliminary to coiling and twisting as in D 
and F. D, Early stage. Twisting of hyphae about one another. E, Early stage, showing symohyo- 
genetic and meristematic tendencies in pycnidial formation. F, G, H. More advanced stages in the 
process of pycnidial formation 



the two being intermediate. Blocks of agar were cut out from the dish, 
fixed, and imbedded in paraffin. A single section frequently includes 
a gradual series of the several stages, from the very youngest to the more 
mature structures. The sections were made both perpendicular and 
parallel to the surface of the agar, the second method proving the more 
satisfactory. 

The young pycnidium as it occurs in agar appears to be made up of 
a closely tangled mass of hyphae. In section the young fruiting body 
is composed of pseudoparenchyma, the cells of which arc closely packed 
and consequently somewhat angular (Fig. 23, h). As is noted by De Bary 
(1887: 247), pycnidia may arise either as intercalary formations on hyphal 
branches by the swelling and division of cells, or by the union and inter- 



■jo Bulletin 379 

weaving of mycelial threads. The former process is termed meristogenetic 
and the latter symphyogenetic. A third possible method, not unknown 
among the fungi, is by a combination of these two processes. 

Potebnia (1910:62), in a note on Sphaeropsis pseudodiplodia (Fckl.) 
G. Del., states that the pycnidia arise meristogenetically. The writer 
was for some time under the impression that this was the character of 
the process, but this opinion was based on observations of later stages 
rather than on the earliest steps in the development. The dense pseudo- 
parenchyma of the maturer fruit bodies suggests meristematic divisions, 
but apparently the structure, for the most part, arises symphyo- 
genetically (Fig. 23). 

In agar cultures a group of threads may be observed to be directed 
toward a common point where the pycnidium is to be formed. Here 
the hyphae are composed of cells from 6 to 7 /* broad, their length varying 
from 20 to 70 ix, always longer than broad. In the region where the 
pycnidium is to be developed, the cells become noticeably shorter by 
the laying down of new walls; the cells also increase in diameter by 
growth, and the hyphae increase their numbers by branching (Fig. 23, a). 
This stage is observed with ease in petri-dish cultures. 

The behavior of the threads in the formation of the pseudoparenchyma 
is varied and the process is somewhat indefinite. The mycelial branches 
that enter into the structure may arise from the short cells (Fig. 23, a), or 
they may grow in from adjacent hyphae (Fig. 23, e). The interspaces 
found in the earlier stages are filled by the growing in of these branches 
and by a budding-like action of the hyphal cells bordering the space 
(Fig. 23, B). 

Serial sections show that there is considerable coiling and gnarling 
of hyphae. Threads may twist about one another for some distance 
in a rope-like fashion (Fig. 23, d). In some cases the threads are localized 
in their intertwining so that the resulting structure becomes a knot or 
ball of densely woven hyphae (Fig. 23, f, g, h ). The formation of such a 
structure necessitates that the hyphae pass into many planes, and in cross 
sections the ends of many hy] ihae present a pseudoparenchymatous appear- 
ance (Fig. 23, h). 

In the intertwining process, hyphae may conjugate in an H-shaped 
fashion. In some cases threads that are parallel probably fuse side by side, 
although the evidence for this is not complete. 

The next important stage is the formation of the cavity. At first 
no differentiation of the closely tangled mass of threads is shown in the 
young pycnidium, but soon the preparation for the cavity is evident. 
Certain cells occupying the central region become more densely granular 
than the surrounding cells. This appears to be the beginning of the 




Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 71 

cavity. Later stages show the breaking down of these cells, and finally 
an oval or a globose cavity is formed. Baccarini (1890:69) states that 
these central cells transform by a mucilaginous process, and that the 
cavity is enlarged by the gelatinous center's absorbing water and exerting 
a pressure on the sporogenous layer. He emphasizes the importance 
of the central "tissue" and expresses the opinion that it has a special 
function, believing that it is destined to become sporogenous whereas 
the outer surrounding cortex only furnishes nourishment to these cells. 

The formation of the ostiole is similar to the process exhibited by the 
development of the cavity. The cells break down, enlarging the passage, 
and finally the wall is definite and continuous with that of the spore cavity. 

The spore-bearing area occupies almost all the space not included 
by the ostiole. The cells lining the cavity 
arch outward, and continued growth results 
in the formation of a stalk. The tip of the 
stalk swells, and ultimately a mature spore is 
cut off (Fig. 24). The further development 
of the pycnospores has been discussed. 

pycnospores. The morphology of the FlG - -4- pycnospore devel- 

1 KJ OPMENT 

pycnospores has been more carefully studied Stages in the f ormationo f a pycno . 
than that of the pycnidia. In the same and spore £rom a «= nid '°P hore 
in different pycnidia on the same and on different plants, wide variation 
with respect to size, color, shape, and.septation have been observed 
(Fig. 25). 

The average mature pycnospore measures about 12 by 25 (i, although 
the range in single or in different pycnidia on the same or on different 
hosts or host parts may be considerable. From the measurement of 
hundreds of pycnospores, it has been found that they range from 7 to 
16.2 n broad by from 16 to 36/1 long, while the averages from different 
hosts range from 9.5 to 13.3 m by 19. 8 to 27.8^. Spores on the apple 
show a slight variation on the different organs, as follows: on the fruit, 
10.6 by 25/n; on the twigs, 11.6 by 23.8 /x; on large limbs, 12.9 by 24.9 yu; 
on the foliage, 12.3 by 23.51*. Paddock (1899b: 195, table 1) notes 
considerable variability with respect to size as the spores occur on 
different plants, but he says: "Yet the spores produced on apple fruits 
inoculated with cultures from either host, are of the same size and 
character; similarly, though not shown in the table, when pear trees are 
inoculated with cultures of Sphaeropsis taken from apple trees the result- 
ing pycnidia and spores are of the average size of those found in nature 
on pear tree bark." 

The mature pycnospores are brownish, varying from a very light to a 
dark ferruginous color. The color darkens with age, so that the very 
youngest mature spores are hyaline. The question of the maturity of 



72 Bulletin 379 

these colorless spores has frequently arisen. The writer has germinated 
them, and is of the opinion that they should be regarded as physiologically 
mature. The hyaline color is replaced later by a yellowish green tinge, 
and finally a brown of varying density is assumed, the spore becoming 
very dark brown in the final condition of coloration, as noted above. 




FlG. 25. VARIATIONS AND TYPES OF PYCNOSPORES OF PHYSALOSPORA CYDONIAE FROM 

VARIOUS HOSTS 

A. Typical unicellular pycnospores; B, typical bicellular pycnospores; C. three- and four-celled pycno- 
spores. not common; D, pycnospores from apple twig: E, pycnospores from apple limb; F, pycnospores 
from a single pycnidium, from apple twig; G, very old pycnospores which have burst; H, pycnospores 
from apple fruit; I, pycnospores from sumac; J, pycnospores from sumac showing peculiar fusion- K, 
pycnospores from sumac; L, pycnospores from crab; M, pycnospores from mulberry; N, pycnospores from 
rose fruits; O. pycnospores from bittersweet; P, pycnospores from rose of sharon; Q, pycnospores from 
witch-hazel; R, pycnospores from spicebush 

The several shades of color may be represented by the spores of a single 
pycnidium, although the majority are uniform in this respect. 

The typical pycnospore is ellipsoidal, frequently tapering slightly 
toward the basal end (Fig. 25, a). The shape also is a variable character, 
however. Pyriform spores may accompany ellipsoidal, globose, or some- 
what elongated forms. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 73 

The question of septation of pycnospores is of importance because of 
the fact that it involves the systematic value of the character, or varia- 
tion if it be so called, in separating the form-genera Sphaeropsis and 
Diplodia, and because of the physiological significance of its formation. 
In nature, three possible conditions exist with respect to the presence 
of one- and two-celled spores. A pycnidium may contain only one-celled 
spores (Fig. 25, a) or only two-celled forms (Fig. 25, b), or both kinds may 
be present (Fig. 2 5 , e , p , q , r) . Occasionally three-celled and even four-celled 
pycnospores have been observed (Fig. 25, c). It is a striking feature in 
this regard that no strain has come under the writer's observation that will 
not produce two-celled spores. Just what factors induce cross-wall for- 
mation is a matter not well understood. Mature unicellular spores placed 
to germinate, whether germinating at once or not, will sometimes develop 
a septum. Again, spores that are found scattered about on the bark of the 
host plant show the bicellular condition. In very dark spores the cross- 
wall is not always readily visible and may be easily overlooked. 

The writer made observations on several strains regarding this character. 
Spores were placed in a drop of water and set in a moist chamber for several 
hours. At the beginning and at the end of each experiment the spores 
were examined for septation. The strains when collected, with the 
exception of one (no. 64)* on mulberry (Morus alba L.), possessed one-celled 
spores only. After being placed to germinate, or in nature after they had 
oozed forth on the substratum, septa began to appear and the percentages 
were as follows: one-celled spores, from two to ninety-five per cent; 
two-celled spores, from five to ninety-eight per cent; three- and four- 
celled forms, rare. The average for all such observations shows that the 
percentage of one- and two-celled forms is about equal. 

Cultural studies were made of an apple strain (no. 82) with reference 
to this and other morphological characters. A single ellipsoidal, brown, 
one-celled pycnospore, 10.8 by 21 n in size, from a pycnidium in which 
all the spores were one-celled and typically like the one described, was 
isolated on March 3, 1913, and a pure culture was developed from it. 
Examination of the culture at intervals showed the development of 
hyaline, Macrophoma-like spores. At the end of twenty-four days these 
had become brownish, and, while the majority were ellipsoidal, averaging 
from 9 to io/i by 21 to 22 m, a few were pyriform and measured 12.6 by 
30.6^. At the end of fifty days an occasional spore was found with a 
cross-wall; after eighty days thirty per cent of the spores were two-celled, 
and on May 27 sixty per cent were bicellular. 

From the same culture a second generation was originated by culturing 
a one-celled, ellipsoidal, brown spore, 11 by 22/u in size. The following 

* The specimens were numbered consecutively regardless of source, host, and other considerations. 



74 Bulletin 379 

notes were taken: Within two weeks an occasional spore measured 7.5 
by 21 ix. although the usual size was from 9 to 10.8^ by 19.8 to 26.1 ll. 
After forty days several two-celled spores appeared. At the end of two 
months, fifty per cent of the spores were one-septate. 

A third generation was initiated by planting a spore from the second 
generation, of the same shape and measurement as the preceding. After 
one month twenty-five per cent of the pycnospores were of the Diplodia 
type. 

Another series was studied, using a two-celled spore from a pycnidium 
in which both one-celled and two-celled forms were present. Within one 
generation a single spore, 10.8 by 21/1 in size, two-celled, brown, ellip- 
soidal, had developed offspring showing the usual color variations — that 
is, from hyaline to greenish, and finally brownish. After eighteen days 
some of the spores measured 12 by 28 ll, the average being 10.5 by 21 ll. 
Septation began to show after five weeks, and within eighty days sixty 
per cent of the spores examined were two-celled. 

Apparently, from a single pycnidium in which the spores are of a given 
type there may develop in succeeding generations a wide variation in size, 
color, shape, and septation. In an early stage the Macrophoma type may 
appear in both size and color; later the Eu-Sphaeropsis type, one-celled, 
brown ; and finally the Diplodia forms. The variable shapes that may be 
found in the generations succeeding a given type indicate that two-celled 
forms may be mere deviations in the life cycle. On the other hand, Brooks 
and DeMeritt (1912:184) report from New Hampshire a large-spored 
form which holds true to its morphological characteristics for several 
generations. 

Markings on the wall of the pycnospores are reported by Griffon 
and Maublanc (1910:312). These authors claim to have discovered an 
undescribed character of the spores of this species, namely, a shagreened 
wall. This character is not reported elsewhere in literature, and has not 
been observed by the writer among the several strains studied, including 
Dr. Peck's type specimens of Sphaeropsis Malorum Peck. 5 

Long, slender bodies, measuring about 1 .5 li in diameter and often 
50 n in length, have been observed interspersed between the pycnospores 
of a strain from apple twigs. They are not of frequent occurrence in the 
experience of the writer. 

mycelium. The mycelium is composed of septate tubes, monopodially 
branched and comparatively broad — being on an average about 4 to 
7 ix in diameter. In the young hypha? cross-walls are rare, but in older 
branches the threads are often short and frequently with bulging lateral 

f - Following the Vienna Code published in 1006 (Wettstein. R. von, Wiesner, J., and Zahlbruckner. A.. 
Verhandlungen des Internationalen Botanischen Kongresscs in Wien, 1905, p. 200), this specific name shouid 
be capitalized. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 75 



■=to^ 



walls. Color is lacking in young aerial threads, but as age increases a 
greenish yellow, then bluish green, brown, and finally dark brown, hue is 
assumed. In mass the mycelium ap- 
pears black. In cultures lacking potas- 
sium a violet tinge has been observed. 
The walls of the hyphag are relatively ex 
thick, and sometimes a decided double 
contour of the membrane is visible. 
The appearance of the cell contents 





Fig. 26. PART OF CROSS SECTION 
OF SCLEROTIUM 

varies, apparently depending 
somewhat on age and nutri- 
tion. Young and well-nourished 
cells are densely granular, while 
older threads contain vacuoles 
and glycogen drops in abun- 
dance. 

sclerotia (Plate xiii, 3, 
and Fig. 26). Sclerotial bodies 
have been found in nutrient 
media of high sugar content 
and in oat agar cultures of 
ascospores from Hamamelis 
virginiana. Walker (1908:38) 
reports the development of 
sclerotium-like bodies resem- 
bling pycnidia on artificial 
media. They have also been ob- 
served by Baccarini (1890:67) 
just under the skin of the 
apple. 

chlamydospores (Fig. 27). Chlamydospores have doubtfully been 
observed by the writer in host tissues. In a few cases a suggestion of 



Fig. 27. 



CHLAMYDOSPORES OF PHYSALOSPORA 
CYDONIAE 



Types of chlamydospores found in pure cultures 



76 Bulletin 379 

such a body was found in apple bark. In old cultures on various artificial 
media, large, thick-walled, intercalary,' brown, spore-like bodies are some- 
times present in abundance. They were also obtained easily by transferring 
bits of mycelium to sterile water. They have been observed in agar cul- 
tures that have become contaminated by bacteria, being found more 
especially near the bacterial colonies. The most striking forms observed 
were on old agar cultures of the strain (no. 6) from Rhus typhina L. 
Similar bodies are described and figured by Hedges and Tenny (1912:16) 
in their studies on Sphaeropsis tumefaciens. These large bodies suggest 
young pycnidia, owing to the form and cellular structure. All gradations 
from thick-walled, colorless, greenish or brownish, granular, swollen cells, 
occurring singly or in chains, are very common in artificial culture. 
These bodies have been germinated by the writer, the germ tubes de- 
veloping into hypha? of the usual type (Fig. 27, near top). 

microconidia (Fig. 2S). Microconidia, or secondary bud-like bodies, 
have been observed in culture after forty-eight hours. They develop 
as swellings near the tips of the growing hyphae. They 
are globose or somewhat pyriform, measuring from 3.6 
to 6.3 n by 7 to 14.5 /u, averaging 4 by 9.5^1. 

yeast forms. Alwood (1S98 b) records the dis- 
covery of a yeast form occurring in the laboratory 
cultures of the fungus, which on isolation and rein- 
oculation of apple fruit produced its fruiting bodies. 
Such forms have never occurred in any of the writer's 
pure cultures. 
MicRoco- The variations exhibited by this fungus do not repre- 
jsporacydoniae sent unic l ue phenomena among the fungi. Shear and 
showing microconidia Wood (1913:63) say of Glomerella: "No character, 

developed on the mycelial -,i 1 1 • 1 1 • 1 • 1 j 1 11 

threads. The three mi- either morphological or physiological, seems to be well 

croconidia in the center r- 1 >> o>l_ £ 1 / *rr r \ • 1 

are magnified 800 diam- fixed. 1 hey find (page 64 ot same reference) wide 
variability in the manner of conidial production; all 
intergradations between a hyphomycetous type and a distinct melan- 
coniaceous type of structure occur in cultures. Seta? may be present in 
some cultures and absent in others, while paraphyses are regarded as of 
little taxonomic value. Duggar (1909 : 303), in speaking of the Alternaria- 
Mucrosporium question, says: " The catenulate method of spore produc- 
tion has been reported only in artificial cultures in this case, and it is 
possible, furthermore, to obtain for various fungi in such cultures in 
general many variations from what would be considered the normal type 
of spore production upon the host." It is stated in the same place that 
cultures of such forms as Fusarium, Gloeosporium. and Cercospora yield 
variable characters in culture. Seaver(i9o8) points out the misleading 




Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 77 

and misused color characters in some of the Hypocreales. Stevens and 
Hall (1909 b) report considerable variation in certain forms under different 
environmental influences. 

PHYSIOLOGY 

methods of isolation. The chief methods used in isolating the 
organism were: the plating of spores in agar and the transfer of single 
germinating spores; transfer of single spores by the capillary tube method 
as described previously by the writer (1913:291-292); planting bits 
of diseased tissue in agar plates. The first two methods are advanta- 
geous in getting pure lines or races. The third method has practical 
advantages in its simplicity and the ease with which the culture is obtained. 

cultural characters — general. The ability of this fungus to 
grow on the commonly used culture media is a noticeable physiological 
character. It is easily isolated, and its appearance in successive stages 
of development is generally the same in all the culture media employed. 
The colonies are at first cottony; after from two to five days the sub- 
merged threads are green or blue-green for about a week, after which 
the growth is dark or nearly black, but almost without exception the 
outer ends of the aerial threads maintain their original cottony appear- 
ance. After from seven to ten days pycnidia appear. The writer has 
always been able to develop pycnidia in culture, although Brooks and 
DeMeritt (1912:183) found considerable difficulty in getting cultures to 
sporulate. Often a distinct concentric zonation occurs in plate and tube 
cultures. The exudation in culture of drops of liquid has been observed 
frequently. This is described by Potebnia (1907), who regards it as an 
excretion product. 

The general characters described above — except zonation, which is 
irregular in its occurrence — apply to the following media: several dif- 
ferent agars, including potato, prune, apple, oat, bean, and nutrient; solid 
vegetable substances, such as potato cylinders, bean pods, apple twigs, 
and apple fruit cylinders; synthetic liquid media, such as Fraenkel and 
Voge's, Cohn's, Rankin's, and Uschinsky's solutions. 

cultural characters — special. The writer (1913:292-293) has 
previously reported differences in the growth of cultures from ascospores 
and pycnospores when planted in +10 nutrient agar. On the one hand 
pycnospores were developed within about one week from pycnospore 
plantings, whereas on the other hand no fruiting bodies had appeared 
after several weeks in cultures from ascospores, the growth remaining 
stunted. Cultures of ascospores and of pycnospores were similar on other 
media (Plate xin, 1). 

protoplasmic streaming. Protoplasmic streaming in the hyphse 
has been studied by Potebnia (1907)- He has found that movement 



yS, Bulletin 379 

begins with the germination of the pycnospore. The direction is first 
toward the tip, some granules moving more rapidly than others. On 
reaching the tip, those that have moved the faster direct their movement 
backward, in some cases forming groups. The streaming is not dependent 
either on evaporation through aerial parts or on the structure of the 
protoplasm, but is conditioned only by apical growth of the hyphae and 
by inner processes. The slow movement is pulsative, and it is observed 
that increased temperature accelerates forward movement and cooling 
often induces backward flow. It is suggested that the streaming is similar 
to the slow movement observed by Van Tieghem in the hyphae of the 
Mucorales. 

PATHOGENICITY 

The ability of the organism to produce the disease, particularly the 
leaf spot and canker forms, has been a matter of no little consideration. 
The difficulties that are met in attempting to infect various plants have 
brought out, not only some conflicting results, but also, what is more 
encouraging, some interesting problems with reference to the causal 
agent and the taxonomic relationship of the so-called species on the 
different host plants. The cross-infection of the several hosts, and the 
role of organisms associated with Physalospora Cydoniae in the production 
of the lesions, are points that have a practical and scientific bearing on 
the whole problem. The different forms of the disease are followed 
in the succeeding discussion. 

black rot of ABPLE. The ability of the fungus to cause decay of 
fruits was established, after a fashion, in 1878 by Peck, who writes 
(1879:20) that "the disease is contagious, and may be communicated 
from One apple to another." 

Von Thtimen (1879) 6 regards the fungus, which he called Diplodia 
Malorum Fckl., as a saprophyte rather than a parasite, but believes that 
it is capable of attacking sound fruit and is able to cause notable injury 
in storage. 

Arthur (1885) inoculated sound quinces by inserting beneath the skin 
a bit of diseased fruit tissue containing spores of the fungus (which he 
calls Sphaeropsis Cydoniae C. & E.). The inoculated fruits were placed 
under a bell jar. Arthur says: "The spores germinated, and the rotting 
progressed slowly, when, on the twenty-second day, the spot had reached 
an inch and a half in diameter, and the fruiting points had begun to appear." 

Halsted (189-2) states that the fungus grows interchangeably on apple, 
quince, and pear fruits. He reports having corroborated his laboratory 
experiments by field observations. 



6 Original not seen by the writer; context takea from Baccarini (1890 : 70). 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 79 

Sturgis (1894) made inoculations both in the field and in the laboratory, 
confirming the work of Halsted (1892) and showing that when the skin 
was not broken previous to inoculation the fruits remained in a sound 
condition. 

Paddock (1899 b: 185) produced black rot of apple artificially within 
a few hours by the use of the black-spored fungus, pycniclia appearing 
after sixteen days. Again, Paddock states (page 193 of same reference) 
that the fungus from pear, quince, and Japanese plum produces rot in 
apple, pear, and quince, if the skin is punctured and moisture is furnished. 

More recent inoculation experiments are reported by Walker (1908), 
Morse (1909), Arnaud (191 2), and others. 

Two forms of Sphaeropsis were observed by Walker (1908), both of 
which were capable of producing black rot — the newer form, however, 
being a more vigorous rot producer. The morphological differences 
have been previously noted. 

The writer made several inoculations (tables 1 and 2) on apples of 
different varieties, using different strains from bark and fruit. In all 
cases pure cultures of the fungus were used. In making wounds to serve 
as infection courts a flamed scalpel was employed. Material transferred 
from the culture consisted of mycelium and spores; this was inserted 
in the injury previously made, and the fruits were placed in sterile moist 
chambers. It is to be noted from table 1 that different strains vary in 
their ability to infect the same variety. Attention is called to a comparison 
of strains 1, 2, 3, and 4. All were used on Baldwin apples on the same 
date and under similar conditions, yet the results were different. Strains 
1 and 3 showed slow decay, with no pyenidia after nineteen days. On the 
other hand, strains 2 and 4 caused rapid decay and abundant pyenidia 
in the same length of time. 

As shown in table 1, nine different varieties were inoculated with the 
same culture, the results being variable with reference to decay, fruit 
body production, and the formation of concentric rings. 

It has been commonly observed that older cultures produce the disease 
less readily than do younger cultures. The best results were obtained 
by the use of cultures not more than two months old. 

leaf spot of apple. Various theories have been advanced to explain 
the cause of the leaf spot disease. In 1902 Stewart and Eustace (1902 : 228) 
believed spray injury to be the responsible agency. They further suggest 
(page 232 of same reference) that drops of rain act as lenses and so con- 
centrate the rays of the sun, overheating the tissues beneath. The belief 
is ultimately expressed by them that the large proportion of leaf spot 
in New York is due to spray injury and is not of fungous origin. Frost 
has been considered the causal factor by Stone and Smith (1903) in 



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Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 83 

Massachusetts. They write: "No organism was to be found as the cause 
of the injury, and from the sequence of events there could be no reasonable 
doubt that the frost was the destructive agency." 

The fungus theory was probably first favored by Alwood (1892:59), 
who attributed brown spot to Phyllosticta pirina. This organism has 
been regarded as the causal agent by several other writers — Kinney 
(1895 b), Lamson (1899), and others. In 1895 Stewart (1896) found a 
new species of Phyllosticta, described as Phyllosticta limitata, responsible 
for an epiphytotic of leaf spot on Long Island. In 1907 the fungus 
Phyllosticta pirina Sacc. was transferred to the genus Coniothyrium by 
Sheldon (1907), and the organism is now designated as Coniothyrium 
pirina (Sacc.) Sheldon. Another species of Phyllosticta, P. prunicola 
Sacc, is listed by Tubeuf and Smith 7 as the cause of spotting of leaves of 
apple, plum, cherry, and apricot. 

Alwood (189S a) records, in addition to P. pirina, other fungi associated 
with the leaf spot, including Hendersonia Mali and Sphaeropsis Malorum. 
This is the earliest record that the writer has seen of the occurrence of 
the last-named fungus on leaves of apple, although Clinton (1902, and 
1904:298) reports it as the common cause of leaf spot in Illinois and 
Connecticut in later years. The question of its relationship to the leaf 
spot disease, as well as that of other fungi, was subsequently studied 
by various pathologists. 

Scott and Quaintance (1907) state that several different fungi, most 
prominent among which are Phyllosticta sp., Hendersonia sp., and 
Sphaeropsis Malorum, are connected with spots and may be responsible 
for the injury in some cases, yet they are not clear as to which are the 
real parasites. The following year the subject was investigated by Hartley, 
I. M. Lewis, and Scott and Rorer. Hartley (1908 b), in examining leaf 
spots of apple from the West Virginia Agricultural Experiment Station, 
found the following fungi: Coryneiim foliicohtm, Coniothyrium pirina, an 
undetermined species of the Tuberculariae, Sphaeropsis Malorum, Mono- 
chaetia Mali, Pcstalozzia breviscta, Phyllosticta limitata, Torula (?) sp., 
Macrosporium sp., Ascochyta sp., Phyllosticta (?) piriseda (?), Phoma Mali, 
Septoria piricola (?), Metasphaeria sp., and an undetermined species of 
Leptostromaceae. He expresses the opinion that probably Coryneum 
foliicolum was formerly reported as a Hendersonia. The fact that the 
parasitism of Coniothyrium pirina was questioned by Stewart and Eustace 
(1902:228) led Hartley to investigate the pathogenicity of this species. 
He found that it would not affect healthy tissue, but that on the other 
hand, when wounds such as scalding, abrasion of epidermis, or punctures 



7 Tubeuf, K. F. von, and Smith, W. G. Diseases of plants induced by cryptogamic parasites, page 463. 
1897. 



84 Bulletin 379 

with hot and cold needles, were made in the tissue, the fungus in most 
cases grew and fruited. He concludes that C. pirina is a facultative, or 
wound, parasite only, and further that its ability to cause leaf spot in 
orchard trees to any extent remains to be demonstrated. In his opinion 
Coryneum foliicolum is less parasitic in the field than Coniothyrium 
pirina. 

I. M. Lewis (1908 : 367.) writes as follows regarding the leaf spot situation 
in New Hampshire: "Believing that the exact relation of all the fungi 
associated with the spots had not been thoroughly tested, an investiga- 
tion was begun during the past summer to determine, if possible, the 
cause of the disease as it occurs in this State, and means of control by 
various spray mixtures." He states further (page 368 of same reference) 
that on isolation it was found that the fungi predominating were Conio- 
thyrium pirina, Coryneum foliicolum, Sphaeropsis Malorum, Altcrnaria sp., 
and one of the Tuberculariae. To Hartley's total list of fungi associated 
with apple leaf spots, C. E. Lewis (1912:51) adds Cladosporium herbarum 
(Pers.) Link and Dematium pullulans De Bary, while Brooks and DeMeritt 
(1912:182) report the isolation of a Fusarium. The first series of experi- 
ments made by I. M. Lewis (1908), on August 1 showed that many inocula- 
tions did not result in infections; from this Lewis reasons that "the 
period at which the leaf is naturally infected is earlier in the spring and 
summer." This view is upheld by C. E. Lewis (1912 : 55), who concludes 
that the older leaves are not so susceptible to infection as are young 
leaves; the work of Brooks and DeMeritt (1912 : 190), however, in which 
they conclude that infection may occur until the last of August, indicates 
that the question of biologic races was a factor overlooked by both 
I. M. Lewis and C. E. Lewis. As regards the general conclusions of 
I. M. Lewis's work it may be further quoted (190S): 

As a result of this season's inoculation experiments it is impossible to offer more than 
negative results as to the cause of the spots. I am of the opinion, however, that the 
fungus Sphaeropsis malorum which is known to cause canker of apple limbs and is an 
active parasite, will be found to be the primary cause of apple leaf spot. This sup- 
position must, however, be supported by direct experiment before it can be definitely 
affirmed for the spots considered in this investigation. 

The same year the results of further investigations by Scott and Rorer 
(1908) were published, in which a definite conclusion was reached. They 
state (page 49 of reference cited): " It was found that Sphaeropsis mal- 
orum, contrary to the general belief, is the cause of the disease." Regard- 
ing the associated species they conclude (page 52 of same reference) : 

Coniothyrium pirina (Sacc.) Sheldon, although it occurs abundantly on apple leaf- 
spots, appears to have nothing to do with their formation. 

The several other fungi that were tested, such as Hendersonia sp., Coryneum sp., 
Pestalozzia sp., and Alternaria sp., proved to be non-parasitic in these experiments and 
probably occur on leaf spots only as saprophytes. 



Black Rot, Leaf Spot, and Canker of Pomaceous "Fruits 85 

The work of Scott and Rqrer is practically confirmed by C. E. Lewis 
(1909). After making several inoculation experiments the latter writes 
(1912:55), in agreement with Hartley (1908 b), as follows: 

The results of these inoculation experiments seem to indicate that Sphaeropsis is 
able to attack the leaves of orchard trees when they are inoculated early in the season 
under favorable conditions for growth. No spotting has been produced by any of the 
other fungi which have been tested although it has been found that they grow readily 
on dead spots which have been killed by other causes. 

The investigations of I. M. Lewis began in 1908 and were continued by 
Brooks and DeMeritt in 1909. As Brooks and DeMeritt state (1912 : 183), 
the summer's work was not conclusive. Later cultural work revealed to 
them great variation in the nature of growth of different strains of the 
fungus, and also in the time required for spore production. It has been 
mentioned elsewhere (page 6S) that these authors found morphological 
strains. This discovery led them to investigate, the correlation between 
the morphological and biological variations of these forms. Their final con- 
clusion (page 190 of reference cited) is: "Several strains of Sphaeropsis 
Malorum may be obtained, varying in general vigor and in power to produce 
diseased conditions. The large-spored form, with single-loculed, ostiolate 
pycnidia is largely responsible for the production of leaf spot." 

The writer performed inoculation experiments in an attempt to produce 
apple leaf spot during the summers of 1910 to 1913 inclusive. In the 
experiments of 19 10 the leaves of mature trees were inoculated in the follow- 
ing manner: Pycnidia were removed from pure culture and the spores 
liberated by crushing the fruiting bodies in a watch glass containing water. 
The contents of the watch glass were removed to an atomizer and the 
spores were sprayed on both surfaces of the leaves. In some cases the 
leaves were previously wounded with a needle, in others they were left 
uninjured. Data regarding the source of the fungus, the variety and age 
of the tree whose leaves were inoculated, the date of inoculation, the number 
of leaves inoculated, and the results, for 1910 to 1913, are given in table 3. 
It is to be noted that no moist chamber was provided in any of the 
experiments of 1910. In 191 1 a series of inoculations made on May 27 
resulted in infection where wounds and moisture were provided. The 
method of work here was the same as in 19 10, except for the provision of 
a moist chamber. This consisted of a lamp chimney, into which the in- 
oculated leaves were inserted and the ends of which were closed with 
damp cotton. The series of inoculations performed in July, 1910, and in 
August, 191 1, should be compared. In neither case was a moist chamber 
used and the results were negative. In the experiments of 1912 and 1913 
no spotting of the foliage was obtained by artificial inoculations. The 
writer has no explanation to offer. The explanation offered by Brooks 



86 



Bulletin 379 



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Black Rot, Leaf Spot, and Canker of Pomaceous 'Fruits 87 

and DeMeritt (19 12) for the leaf spot problem in New Hampshire is 
apparently not applicable under western New York conditions, since a 
variety of morphological forms was used in the inoculation work. The 
results obtained indicate that there is no correlation between morpho- 
logical and biological characters with respect to pathogenicity. 

canker of apple. Waite (1898 a) was the first to attribute the canker 
to a fungous parasite; he suggested that Schizophyllum commune Fr. was 
the causal organism. Paddock (1899 b: 183) found dark spores on the 
cankers, but supposed they belonged to some saprophytic form. How- 
ever, he grew this organism, as well as Schizophyllum commune, on artificial 
media, and made pure culture inoculations in the following manner: A 
small opening was made in the bark by means of a sterilized knife, and a 
small quantity of material from bean stem cultures was inserted between 
the wood and the bark. The incision was covered with moist filter paper 
and kept moist for thirty-six hours. All the inoculations made in 1898 
with the dark-spored fungus on apple trees were successful; other fungi 
failed and the wounds soon healed. Paddock's conclusions are sum- 
marized in the following words (page 184 of same reference): "These 
experiments showed conclusively that the dark-spored fungus can pene- 
trate living apple-tree bark under certain conditions and produce a 
cankered condition of apple-tree limbs and also indicated that it may pro- 
duce a diseased condition of pear-tree bark." Again he says (page 185 of 
same reference): " The result of over fifty inoculations made from cul- 
tures that were obtained from cankered apple tree limbs prove that the 
apple-tree canker of New York apple orchards is caused by a fungus of 
the genus Sphaeropsis." Over one thousand inoculations were made by 
him in 1899 (pages 200-201 of same reference) and only a very few gave 
negative results. He further asserts that the fungus causes canker of the 
quince if the material from pure culture is inserted under the bark, 
whereas under other conditions the experiments were not conclusive. 

Paddock's work was continued (1900) for the purpose of confirming 
former results and to determine if possible the relationship between the 
species of Sphaeropsis that occur on various plants. He obtained cultures 
from apple fruit and apple bark, and inoculated the apple tree and other 
plants. The results were positive, thus further proving the pathogenicity 
of the organism, as well as establishing the identity of the fungus on fruit 
and bark. The conclusions reached by Paddock are essentially con- 
firmed by C. E. Lewis (1909:188-189) and by McCready (1910). 

The writer (1913:293) has summarized the results of earlier inoculation 

work as follows: 

During the past summer [1913J several inoculations have been made with cultures 
from the ascospores of the ascomycetous fungus. The apple, pear, quince, crab apple, 
and other plants were inoculated, in each case wounds being made to serve as infection 



88 Bulletin 379 

courts. Three varieties of apples, namely Twenty Ounce, Baldwin, and Chenango 
Strawberry, were inoculated between May 20 and July 16, 1913. Eleven sets of experi- 
ments involving about seventy incisions were made, all of which gave positive infections, 
the checks remaining healthy. 

The above quotation concerns the ascomyeetous fungus from apple. 
A morphologically similar organism on Hamamelis virginiana did not 
produce infection, as is seen from the following statement (Hesler, 
1913:293): "About twenty-five different inoculations were made [with 
the ascomycete from H. virginiana] on all the plants mentioned above 
but no infections occurred." 

The writer has carried on inoculation experiments during the past 
four years, both in the greenhouse and in the field, the most of the work 
being directed toward the infection of bark tissues. The methods employed 
have already been described (page 79). The results discussed at this 
point concern only experiments in which apple strains of the fungus 
{Physalospora Cydoniae Arnaud [ = Sphaeropsis Malorum Berk.]) were 
used on apple itself. The more important points in this regard are shown 
in table 4, indicating the source of the strain, the variety and age of the 
tree inoculated, the conditions under which inoculations were made, the 
number of inoculations, and the general results. The infection work done 
in the summers of 1910, 1911, and 1912 was not conclusive, but with 
the use of various strains more satisfactory results were obtained in the 
season of 19 13. 

It may be noted in table 4 that races of the fungus came from different 
varieties of apple, isolations being made from fruit, leaf, and bark. It was 
desired to determine if possible whether strains obviously living under 
saprophytic conditions, as those following winter injury and fire blight, 
were capable of inducing bark injury, and to determine the nature 
of the parasitism of certain other strains that appeared to be parasitic. 
The results on these points are conflicting and it seems that the strains 
are as variable in their biological relationships as in their morphological 
characters. A race may produce infection on slightly wounded bark 
after it has been living under saprophytic conditions, for example, following 
fire blight. Again, those strains which in nature appear to be acting 
parasitically may prove to be weak parasites, producing infection only 
under certain conditions. 

Conflicting results along this line have raised the question of individual 
variation among varieties of the host plant as regards susceptibility or 
immunity. It is possible that individual hosts in the same or in different 
orchards may differ in this respect, but conclusive data are not at hand 
with which to answer the question. 

The variable results of inoculations of the apple with the apple fungus 
indicate that the production of infection requires the proper strain, a 



Black Rot, Leaf Spot, and Canker of Pomaceous Pruits 89 



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3. Limb 5 cm. in diameter, 
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Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 95 

wound in which to initiate the relationship, and moisture until infection 
has occurred. 

Associated species. — It has been noted elsewhere that the fungus 
Schizophyllum commune Fr. was suspected as being the cause of canker 
(Waite, 1898 a). This apprehension was undoubtedly based on asso- 
ciation of the fruiting body of the organism with the lesions, as it is common 
to find this fungus fruiting on old cankered limbs. Paddock (1898 a) 
cultured this species and after inoculating apple limbs concluded that 
it was not the cause of the disease. 

The role of associated species in the production of canker on apple 
is taken up somewhat at length by C. E. Lewis (1912). In Maine the 
fungi most frequently found on dying twigs and branches of apple are 
Sphaeropsis Malorum, Myxosporium corticolum Edgerton, Coryneum 
foliicolum Fckl., Cytospora sp., Phoma Mali Schulz & Sacc, and Conio- 
thyrium pirina (Sacc.) Sheldon. Those often developing in plate cultures 
were: Phyllosticta limitata Peck, Dematium pullulans De Bary, Clado- 
sporium herbarum (Pers.) Link, Alternaria sp., Macrosporium sp., Fusarium 
sp., Epicoccum sp., and Glomerella cingulata (Stonem.) Sp. & von Sch. 
To this list the writer adds Septoria sp., Cephalothecium roseum Cda., and 
Aspergillus sp. C. E. Lewis (1912:62) concludes "that Coryneum and 
Phoma can cause considerable injury to young trees and branches of 
orchard trees. Myxosporium and Cytospora do not attack healthy 
branches but it seems probable that they attack weakened branches." 
The writer's results with the various associated fungi may be summarized 
by the statement that none of the species enumerated above made growth 
on apple bark. 

CROSS-INOCULATIONS AND HOST RELATIONSHIPS (Plates VIII, IX, XI, Xiv). 

The identity of the various species of Sphaeropsis on the same and on 
different plants has been established in certain cases. That the species on 
the fruit of apple is the same as that on the bark was proved by Pad- 
dock (1899 b, 1900) several years ago, and confirmed by Potebnia (1907) 
more recently. A similar relationship for the fruit and foliage forms 
of the fungus has been proved by Morse (1909), while Scott and Rorer 
(1908) have demonstrated the identity of the organism on leaves and 
bark. The ability of these three forms to grow interchangeably on the 
several organs of the apple is no longer questioned, and the results of 
previous investigations are essentially confirmed by the writer in tables 
1, 2, 3, and 4. 

The pycnidial stage of Physalospora Cydoniae Arnaud {Sphaeropsis 
Malorum Berk.) has been collected by various investigators (Paddock, 
Arnaud, the writer, and others) on the following plants: apple (Pyrus 
malus L.), apricot (Prunus armeniaca L.), alder (Alnus glutinosa Gaertn.), 



9 6 



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98 Bulletin 379 

ash (Fraxinus americana L.), basswood (Tilia americana L.), bittersweet 
(Celastrus scandens L.), box elder {Acer negundo L.), cherry (Primus 
avium L., P. pennsylvanica L., P. virginiana L.), cherry laurel (Primus 
lauro-cerasus L.), crab (Pyrus coronaria L.), currant (Ribes sp.), dogwood 
(Cornus stolonijera Miehx., C. sanguined L.), elder (Sambucus cana- 
densis L.) , elm ( Uhnus americana L.) , fig (Ficus carica L.) , grape ( Vitis sp.) , 
hawthorn (Crataegus oxyacantha L.), hop hornbeam (Ostrya virginica 
[Mill.] K. Koch), lilac (Syringa vulgaris L.), maple (Acer saccharinum L.), 
mulberry (Morus alba L.), oak (Quercus alba L., Q. prinus L.), osage 
orange (Madura pomifcra [Raf.] Schneider), peach (Prunus persica 
[L.] Stokes), pear (Pyrus communis L.), persimmon (Diospyros 
virginiana L.), pine (Pinus strobus L.), plum (Prunus domestica L., P. 
triflora Roxbg.), quince (Cydonia vulgaris Pers.), rose (Rosa canina L., 
Rosa sp.), rose of sharon (Hibiscus syriacus L.), spicebush (Benzoin 
aestivale [L.] Nees), sumac (Rhus typhina L., R. glabra L.), sycamore 
(Platanus orientalis L.), witch-hazel (Hamamclis virginiana L.). Where 
fresh material was available the writer cultured the fungus from all these 
plants except three — dogwood, lilac,, and rose of sharon, which have just 
been collected — and these cultures were used in all cross-inoculation 
experiments. The source of the cultures used, the plants inoculated, and 
the results, are shown in table 5. The methods used were similar to 
those described in connection with the inoculation experiments on apple 
fruit (page 79). In some of the earlier experiments a moist chamber 
was used consisting of a petri-dish lid, the inner margin of which was lined 
with damp cotton. Later the glass lid was eliminated and a cotton cap, 
made by rolling a strip of cotton about the finger, was employed. Moisture 
was provided at the time of inoculation and was added daily for several 
(usually from three to seven) days subsequently. 

The results of cross-inoculations were not conclusive, particularly in 
cases in which the fungus failed to develop. Failure to produce infection 
may be accounted for in two ways: either the fungus was not parasitic 
on the plant inoculated, or conditions favorable for infection were lacking. 
In many cases further trials are desirable. 

In nature the fungus rarely shows a parasitic tendency on wild plants — 
with the exception of Quercus prinus (see Rankin, 1914) — but it is 
generally found developing on dead and fallen twigs; cankers have not 
been observed which could with certainty be attributed to this organism. 
On cultivated plants it commonly shows the same habits as it does on wild 
plants, or it may develop in healthy tissues, resulting in the formation 
of a canker. Here, then, on' the cultivated plants are found both sapro- 
phytic and parasitic tendencies. This phenomenon is in accordance with 
the commonly accepted theory that parasitism originated from sapro- 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 99 

phytism. This is what is to be expected; and the theory is further sup- 
ported by inoculation data which show that the strains from wild plants 
may be induced to infect cultivated plants. The reverse process — that 
is, the infection of wild plants with strains from either cultivated or wild 
forms — has been almost wholly unsuccessful in the writer's experience. 
This in the main confirms the work of Paddock (1899 b, 1900). 

On certain wild plants there is found a saprophytic race which, when 
carried to cultivated forms such as the apple or the pear, acts as a wound 
parasite. On cultivated plants the fungus follows fire blight and winter 
injury, and hence is a saprophyte, but the latter strains are not necessarily 
obligate saprophytes since they have been induced to cause canker by 
artificial inoculation. This is shown by strains 22, 38, 57, and 70 in table 4. 
It does not appear, therefore, that the fungus can be segregated easily 
into physiological groups, since varying degrees of parasitism are exhibited 
by a given race. 

From the experiments described and tabulated it is clear that there is 
considerable variation in the virulence of races, but just how long a given 
parasitic strain will retain this mode of life is a difficult question to answer. 
The ability of the organism to act as a wound parasite, and to adapt itself 
naturally to the saprophytic mode, makes it a serious pest from the stand- 
point of control. Its ability to remain saprophytic indefinitely until the 
host is injured in some way only increases the difficulty in alleviating the 
disease. 

names and synonymy 

The work that has been done on cross-inoculations and on the mor- 
phology of Sphaeropsis from several different plants makes it apparent 
that there is one large polymorphic species. It is true that many inocula- 
tions failed, and that two given races may differ widely in their mor- 
phology; but there is considerable evidence that these characters are 
variable and are not important in taxonomic considerations. 

The several forms as they have been described from time to time have 
been given a specific name, usually one for every host plant. This pro- 
cedure has resulted in the accumulation of a large number of specific 
names which could now be disposed of only by the examination of type 
material of each so-called species. Several generic names have become 
involved in the synonymy of the fungus, due to the indefinite limitations 
and wide variations, and consequent overlapping, of certain form-genera. 
Saccardo (1884 a) believed Sphaeropsis Malorum Berk, to be a Phoma, 
since it was originally described by Berkeley (1836) as having yellowish 
green spores. It is now known that the young spores have this color 
characteristically, and furthermore Dr. C. L. Shear, who has seen Berkeley's 



ioo Bulletin 379 

type, has stated (in conversation with Dr. Donald Reddick, of Cornell 
University) that the organism is unquestionably identical with Sphaerop- 
sis Malorum as now recognized. Subsequent to Saccardo's use of the name 
Phoma, this genus was divided into Phoma and Macrophoma — the former 
genus containing species with spores less than 1 5 /j. long, the latter con- 
taining species with spores more than 1 5 ^ long. Thus Phoma Malorum 
(Berk.) Sacc. was renamed by Berlese and Voglino (1886) as Macrophoma 
Malorum (Berk.) Berl. & Vogl. 

It appears that certain species of Sphaeropsis have been confused with 
those of Diplodia. The two genera are separated on the basis of one- 
celled spores in the former and two-celled spores in the latter. But 
both genera fail in their chief distinction, so that mycologists have been 
misled on this point. Fiickel (1869:393) used the name Diplodia pseudo- 
diplodia Fckl. in describing the fungus on branches of apple; elsewhere 
(page 395 of same reference) he used Diplodia Malorum Fckl. 

It has been noted previously that the pycnidium sometimes approaches 
and even reaches the condition characteristic of the form-genus Botryo- 
diplodia. It becomes evident that the names of certain species of this 
genus may stand only as synonyms of Physalospora Cydoniae Arnaud. 

The origin of several of these synonyms has been discussed in an earlier 
paper by the writer (1912), to which the reader is referred. At that time 
it seemed desirable to attempt the selection of the name that should, 
according to the rules of priority, be applied to the pycnidial stage. 
Recently, however, the perfect stage of the fungus has been found, and thus 
the selection of a specific name from the pycnidial forms is of minor 
importance. The generic name now becomes Physalospora, and the 
writer has chosen Cydoniae as the specific name. The following state- 
ments bearing on this question are quoted from another paper by the writer 
(1913:295): 

The problem of selecting a specific name is somewhat perplexing. The organism 
with which the writer is dealing strongly resembles P. Cydoniae Arnaud but we have 
not seen his type material and there remains the question of whether his fungus has not 
been previously described. In this connection a few species which suggest this possi- 
bility may be noted: P. entaxia E. & E., P. festucqe (Lib.) Sacc. and P. nigropunctata 
Romell, the last on limbs of Pyrus mains according to Saccardo. Until further data 
are at hand the writer is inclined to accept tentatively the name Physalospora Cydoniae 
Arnaud. 

Soon after the above-mentioned paper appeared in print, the writer 
received from Arnaud a glycerin-jelly mount of his type material. It 
is clear that morphologically the organism is identical with the one 
described by the writer (1913) under the same name. But the question 
of the specific name is still unsettled, for it is not improbable, as stated 
above, that the organism has been previously described under some other 
specific name. This problem, as in the case of the several pycnidial 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits ioi 

forms, would involve the study of type material, which as yet has not 
been available to the writer. Under the circumstances Arnaud's specific 
name will be retained tentatively by the writer. The following is a 
partial list of species which are concerned in the synonymy of the fungus ; 
citations to literature are also given: 

Physalospora Cydoniae Arnaud. Ecole Nat. d'Agr. Montpellier. 
Ann. 12: 7. 191 2. 

Sphaeria sumachi Schw. Amer. Phil. Soc. Trans, n. s. 4:205. 1834. 
Sphaeria rhuina Schw. Amer. Phil. Soc. Trans, n. s. 4:218. 1834. 
Sphaeria pomorum Schw. Amer. Phil. Soc. Trans, n. s. 4:219. 1834. 
Sphaeria Malorum Berk. English Flora 5:257-258. 1836. 
Diplodia pscudodiplodia Fckl. Symbolae Mycologicae, p. 393. 1869. 
Diplodia Malorum Fckl. Symbolae Mycologicae, p. 395. 1869. 
Sphaeropsis Cydoniae C. & E. Grevillea 6: 84. 1878. 
Sphaeropsis Malorum Peck. Sylloge Fungorum 3:294. 1884. 

Several years ago Ellis (1880) studied the variability of Botryosphaeria 
fuliginosQ (M. & N.) E. & E. [= Sphaeria Quercuum Schw.], and came to 
the conclusion that this species really included at least eighteen so-called 
species. Among these may be noted, using Ellis's nomenclature, Sphaeria 
entaxia C. & E. [= Physalospora entaxia Sacc], S. viscosa C. & E. [■= P. 
viscosa Sacc], 5. erratica C. & E. [= P. erratica Sacc], Botryosphaeria 
pustulala Sacc, and others. Ellis found wide variation with respect to 
stromatic formation. Sometimes the perithecia were scattered and 
distinct, and again they were confluent and united in a stroma. Consider- 
able range with respect to the ostiolum is also noted by Ellis (1880). But, 
as stated by Ellis and Everhart (1892:547), certain forms of Botryo- 
sphaeria fuliginosa — those lacking a stroma — are removed to the genus 
Physalospora. It may be that under certain conditions P. Cydoniae 
develops a stroma, but such a tendency has not been observed; for this 
reason the generic name Physalospora is selected. 

LIFE HISTORY STUDIES 

The mature morphological structures of the fungus have been described, 
so that the following paragraphs concern only the successive stages in its 
development: where and in what condition the organism hibernates, the 
manner in which it is disseminated, its entrance and effects on the plants 
attacked, and the development of certain of its fruiting bodies. 

source of the inoculum. The fungus passes the winter as mycelium 
in the tissues of the host and as pycnospores in pycnidia. If a canker 
is examined in the spring when growth is resumed by the host plant, 
the margin of the old lesion may show discoloration. The writer has 
frequently planted bits of the bark from the edge of a canker in agar 
plates, pure cultures resulting. This is evidence of the resumption of 
growth of the mycelium in the old lesion. It is stated by Caesar (1909) 



io2 Bulletin 379 

that as a rule the fungus does not die out but continues to extend in every 
direction year after year, finally girdling the limb. In this connection 
Paddock (1899b: 189) writes as follows: "In some instances the 
mycelium apparently lives over winter and continues its growth the 
following spring. The formation of the largest cankers can scarcely 
be explained in any other way." He adds, however, that "in all of the 
inoculations made in the spring of 1898, in only one instance did the 
resulting canker enlarge any during the present season." 

The writer's experience in this regard is somewhat similar, although 
more cankers have enlarged the second year than is intimated by Paddock. 
On this point there appears to be a difference in orchards. In one orchard 
the author counted forty cankers on three trees on May 20, 1912. All 
were formed at least one year previously, but only one showed advance- 
ment at the margin on this date. In other orchards a majority of the 
cankers were enlarging. The vitality of the trees does not seem to 
explain the difference displayed, since this quality appeared similar in the 
two cases mentioned. The trees in the two orchards were of the same 
variety (Twenty Ounce) ; here the question of physiological races may 
throw light on the subject. 

It has been suggested that the mycelium may winter over in mummified 
fruit, and that in cases in which the fruit hangs on the tree the hyphas 
may pass into the branch supporting it (Anonymous reference, 1899 c, 
page 126). The latter condition has not been observed by the writer. 
In some cases the mycelium hibernates in the mummified fruit, but the 
passage of the hyphae down into the branch and the resulting development 
of a canker is questionable. 

The growth of the mycelium at the edge of a lesion, as described above, 
does not account for new and isolated cankers. The phenomenon results 
nevertheless, indirectly, in a source of inoculum, in that fruit bodies may 
develop on the newly infected margin and so furnish spores which may 
cause other infections directly. The young cankers originate by the 
agency of the spores of the fungus. 

It is a common thing to find, in the winter and spring, pycnidia bearing 
mature spores on mummified fruits. These fruiting bodies may be 
observed also on cankers and on fallen twigs, bark, and leaves. In western 
New York cankers and dead twigs are the most important sources of 
the inoculum. 

The hibernation of pycnospores on the various organs of the tree is 
reported by a number of investigators: on the bark, fallen twigs, and 
cankers, by Paddock (1899 b: 189), by Brooks and DeMeritt (1912:189), 
and by Scott and Roret (1908:52); on fallen leaves by Reed and Cooley 
(1911); on the fruit, as mummies hanging on the tree or fallen, by Scott 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 103 

and Rorer (1908:52) and by Brooks (1909). Other writers have con- 
finned all these observations. These spores in winter have been placed 
in room temperature, and were subsequently found to be capable of 
germination in tap water. There is evidence that pycnospores may 
also winter over scattered about on the bark; they have been found in 
early spring before the pycnidia have entered their period of spore discharge. 

The role of the ascosporic stage in hibernation is not certain. As 
previously indicated, the perithecia are rare on Pyrus mains in New 
York, and it would seem, therefore, that the ascospores from this source 
are of relatively little importance in initiating infections. Whether 
this stage is common on other plants in this State, and important as 
a source of inoculum, are matters remaining to be investigated. 

method of spore discharge. The manner in which the pycnospores 
escape from the pyenidium has not been fully described, so far as the 
writer knows. Berkeley (1836) makes mention of the process as follows: 
"When dry the ostiolum is frequently crowned with a short minute ten- 
dril oozing out from the peritheciuin." Halsted (1892) writes: " The 
ripe spores .... form long, slender coils as they are pushed 
out of the small hole in the skin." Similar descriptions of the process 
are given by Clinton (1902) and by Evans (19 10). 

If a bit of bark or of fruit bearing pycnidia is placed under moist con- 
ditions, in a few hours dark masses of spores in the form of a coil may be 
seen (Plate xiii, 4). In one experiment the following notes were taken: 
"Twigs of an apple strain (no. 82) bearing mature brown pycnospores 
were placed in a moist chamber on May 20. 19 13, at 3 p. m. By noon 
on May 23 the dark masses could be seen with the naked eye. These 
masses measure about 200 to 250/1 by 400 to 450 ju." At this time it 
was observed that the masses stood out from the surface of the bark 
nearly five millimeters. They were very easily removed by a needle 
and examined under the microscope. It was observed that on the side 
of the mass nearest the bark several spores had germinated, and the 
resulting hypha? had raised the mass away from the surface of the bark. 
A drop of water was added to one mass, which behaved as follows: In 
a few seconds the mass began to segregate, and single spores or groups 
of a few moved very quickly, with a darting motion, from the mass. They 
were at first thrown through the drop of water as far as 85 n and they 
then moved slowly away. After forty-five minutes the spores had scattered 
in all directions, from 1500 to 2800 yu from the original point of departure. 
The coil in some cases contained about 1500 mature spores and in some 
experiments proved to be at least one millimeter in length. It has been 
estimated by the writer that there may be as many as 150 pycnidia on 
a square centimeter of the surface of an apple fruit; this would furnish 



104 Bulletin 379 

approximately 225,000 spores for the given unit area, or 1,406,250 spores 
per square inch of apple surface. 

As stated in the notes quoted above, the spore coils were found on the 
bark three days after moisture was supplied. But this does not mean that 
all this time was involved in the process of escape. The pycnidia were 
found to be closed at first and considerable time must have been con- 
sumed in their opening. In other experiments as long a period as five 
days was necessary to effect the opening in some cases. The time that 
actually intervenes between admission of moisture to the spore mass 
within the pycnidium and the coiling of the spores is negligible. Pycnidia 
have been removed from dry bark in the summer, placed on dry slides, 
and observed with the microscope. If a drop of water is then applied, 
the spores will ooze out immediately provided the ostiole is open. Their 
fate after coiling seems to depend on the amount of moisture present. 
If a beating rain is falling, undoubtedly the spores are earned by the 
spattering drops toward the ground and perchance lodge on the foliage 
or on the branches. In case of a dew, unquestionably the coil behaves 
as described above; that is, some of the spores on the lower side of the 
mass germinate, the resulting weft of germ tubes raising the spores from 
the bark, when they may be lifted by the wind. Again, if the mass 
encounters a drop of water the gelatinous material quickly expands and the 
spores are scattered throughout the drop. It is conceivable that the 
drop may be carried by the wind for a short distance at least. 

time of spore discharge. The time of the year when spores are dis- 
seminated may be approximated by noting the date of the first appearance 
of the diseased spots, and by keeping careful watch of the behavior of the 
pycnidia in the field. It is believed by I. M. Lewis (1908) that the period 
when foliage is naturally infected is early in the spring and summer. The 
same opinion is expressed by Brooks (1909), who states that the indi- 
cations are that leaf infection ceases in June. Later, however, Brooks 
and DeMeritt (1912:189) attach little value to this statement, expressing 
the opinion that the nature of the fungus was a factor overlooked by 
previous investigators and that weather conditions may play a part in 
determination of the time of infection. 

Paddock (1899 b: 189) states that many spores remain in pycnidia until 
the following spring, when they are disseminated. Wolf (1910I has made 
a study of the prevalence of fungus spores in orchards by exposing agar 
plates, and his conclusions are expressed as follows (page 202 of reference 
cited) : "At no time during the period in which exposures were made 
(September to May, inclusive) were viable spores of Sphaeropsis malorum 
present in the atmosphere of the orchard." McCready (19 10) reports 
mature spores as being disseminated from cankers as early as the first 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 105 

week in April, and states that at the same time a large number of spores 
were found in the orchard on rotten apples. In Virginia, at Blacksburg, 
Reed and Cooley (191 1) found spores being discharged from pycnidia on 
leaves on June 25, 1910. Whether spores are liberated at an earlier date 
these authors do not state, but it is probable that such is the case. 

From observations made by the writer it seems that the date of 'first 
discharge in the spring varies with the season. Apparently the ostiole 
does not open at a temperature below 60° F. (15.5° C.) or in the absence 
of moisture, and a period of humidity of several hours duration is neces- 
sary. The dates for spore discharge observed at Byron, New York, 
are May 16, 191 2, and May 12 and 23, 191 3. In 1911 spores were found 
coiling on July 17, but the process must have occurred earlier. That 
they continue to be liberated throughout the summer is shown by the 
appearance of new infections on foliage from May until September 20, 
1913. In 1911 several young spots were found on bark in the middle of 
August. Ripe and green fruit infections also show that spores are dis- 
seminated in August and September. 

agents of dissemination. It is clear that the behavior of the 
pyenospores on being discharged places them at the disposal of wind, rain, 
and possibly insects, depending largely on the conditions of moisture. 
Halsted (1892) states that "the germs pass .... through the air 
or by means of the various insects that visit the fruits, especially those with 
broken surfaces due to partial decay." A similar opinion is expressed by 
Sturgis (1894). Lamson (1902 : 76) states that the spores are easily floated 
in slight currents of air, while Bethune (1909:29) and McCready (1910) 
attribute dissemination to the wind. 

The writer has observed numerous cases of the disease in isolated situa- 
tions. In some orchards there was abundant leaf spot but no cankers 
were on the trees. Here the wind probably acted as the agent, carrying 
the spores from plants outside the orchard. That the rain washes the 
spores to the foliage is shown by the cone-shaped area of infections beneath 
cankers and diseased fruits. 

Insects are no doubt agents in the dissemination of the organism. The 
gelatinous nature of the spores renders them sticky and they may adhere 
to the feet of insects. In June, 1913, the writer found spores on the feet 
of the rosy apple aphis (Aphis sorbi Kaltenbach), but it is his opinion 
that insects are of little importance in carrying the spores. Their role 
in making openings in the fruit and bark is probably much more important. 

infection courts. The fungus shows little preference for any par- 
ticular type of injury as a means of entrance. It is not able to penetrate 
healthy tissue of the bark and fruit, but follows other fungi such as 
Glomerella cingulata (Stonem.) S. and vS. on fruit, as noted by Alwood 



io6 Bulletin 379 

(1902:257). Other points of entrance to fruit, as listed by Burrill and 
Blair (1901), are insect punctures, mechanical injuries, and the blossom 
end of the apple. These authors state also that the fungus seems to start 
without the aid of a wound. The writer has noted many cases in which 
young lesions on the apple surrounded an opening made by the codling 
moth (Carpocapsa pomonella L.). Delacroix (1903 a: 140) is disposed 
to believe that in some cases certain insects are able to rupture the bark, 
especially that of young branches. He observed an abundance of Epidi- 
aspis piricola (Del Guer.) Ckl. on infected areas, and is of the opinion that 
these insects are concerned here. Gtissow (191 1) states that "apples 
are infected through some injury (wasps, curculio, hail, etc., etc.)." 
Arnaud (19 12) believes that there is some connection between the entrance 
of the fungus, and a beetle. 

Observations show also that various mechanical injuries commonly 
serve as points of entrance for the fungus. Such injuries as limb and 
hail bruises may act in this capacity. Faurot (19 12) states that rot 
occurs largely on fruits the skin of which was previously broken by spray 
injury and growth cracks. 

Whether the healthy epidermis of the fruit is penetrated, as suggested 
by Burrill and Blair (1901), is open to question. The writer has never 
been able to infect unbroken tissues of the apple fruit. On the foliage, 
artificial inoculations by various investigators — Scott and Rorer (1908), 
Brooks and DeMeritt (1912), and others — show that the fungus can 
penetrate healthy leaf tissues. The author, however, has never been 
successful in producing leaf spot without first wounding the tissue. Infec- 
tions in the bark apparently occur only through some sort of wound. 
Such injuries may be caused by growth cracks, as noted by Caesar (1909) ; 
by ladders and boots, in pruning and picking; by barking by the machinery, 
in cultivation; by props not carefully wrapped; by hail; by openings left 
by the careless removal of water sprouts; and in other ways. Of fifteen 
young cankers observed by the writer on a single tree, ten had their origin 
in openings left by the removal of suckers. The writer has observed 
cases in which the fungus had followed the rust fungus, Gymnosporangium 
Juniperi-virginianae Schw., on apple twigs. Scott and Rorer (1909: 11) 
suggest that it may follow Phyllosticta solitaria E. & E. on apple buds. 
The writer has frequently isolated the fungus from lesions caused by 
the blotch fungus (P. solitaria) on apple fruits sent from Indiana. As 
previously noted, the fungus frequently follows fire blight and winter 
injury. Morse and Lewis (1910) state that in Maine orchards much of 
the disease that was called canker had its origin in frost spots of 1906- 
1907, and that so far as investigated the cankers of fruit trees in Maine 
orchards had their origin in wounds. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 107 



pycnospore germination (Fig. 29). The pycnospores usually ger- 
minate readily in tap or rain water. The time required for the process 
varies considerably, depending, no doubt, on the age of the spores. If they 
overwinter, the question of their longevity arises. As a rule sexual spores 
are regarded as short-lived, but it is not so in the case of this fungus. 
Duggar (1909:353) says: "The spores seem to retain their vitality for a 
considerable period of time, having been germinated after being stored for 
a year in the laboratory." The writer has found that spores two years old 
or older may germinate in tap water after twenty-four hours. Younger 
spores ordinarily germinate within five or six hours, but they may pro- 
duce a tube after three hours. Spores which are dark brown in color, 
often septate, and having 
an older appearance, re- 
quire more than twelve 
hours for germination. 

Usually one or two 
tubes emerge from a 
spore at or near the end ; 
germinations also occur 
at the side. The de- 
veloping hypha? in cul- 
ture occasionally form 
microconidia, or second- 
ary conidia, near the 
growing point of a hypha ; 
these have been men- 
tioned by* D e 1 a c r o i x 
(1903 a: 139), who states 
that they do not develop 

further. The writer has germinated them in tap water. In some cases 
peculiar types of germination occur, short, stunted tubes being developed. 
In other cases the process is entirely inhibited, and in certain of these 
cases the laying down of a cross-wall takes place instead. In one obser- 
vation notes were made as follows : 

Spores one-celled when collected (May 13, 1913). Placed to germinate in tap water 
and after twenty-four hours the two-celled spores had not germinated; the one-celled 
spores had developed tubes about 30 ji long. After forty-two hours some of the two- 
celled spores developed tubes about 175^ in length, whereas the germ tubes of the 
one-celled forms were about 500/1 long. 

Again, spores placed to germinate, instead of producing a germ tube, 
after several days developed a septum. Another peculiar behavior of the 
spores is that they may fuse in pairs. Delacroix (1903 a) describes a 
peculiar type of germination of young and hyaline pycnospores in a 




Fig. 29. 



TYPES AND VARIATIONS OF PYCNOSPORE GERMI- 
NATION 



io8 



Bulletin 379 



solution of 2.5 per cent of glucose and 1 per cent of peptone. No cross- 
wall was developed. After the third day the wall broke and the contents 
emerged, forming a bud on the surface of the spore. This spherule may 
attain a diameter of from 35 to 40 /x; its further development was not 
followed by Delacroix. The writer has observed similar behavior of 
pycnospores, except that the swollen parts finally developed a germ 
tube. This took place in tap water. In some cases older spores burst 
and fail to send out a germ tube. 

The effect of low temperatures on pycnospore germination was noticed 
in the spring of 19 13 in connection with infection experiments. On May 
15, 1912, spores in drops of tap water on a glass slide were placed in a petri 
dish, plenty of water was supplied to prevent drying out, and the culture 
was placed out of doors, where the temperature ranged between 8° and 
10° C. A second culture was kept at room temperature (21 C). No 
germinations occurred outside, but the cultures kept in the laboratory at 
21 C. gave normal germinations. On May 12, 19 13, the minimum tem- 
perature was 9 C, the maximum 15.5° C. All spores out of doors failed 
to germinate at these temperatures, while those at 21 C. gave normal 
germination. On May 13,- 19, and 20, 1913, when the maximum tempera- 
ture was i5-5° C, similar results were obtained, except that in one culture 
on May 20, at 15.5° C, a very low percentage of germination was observed. 

This indicates that in most cases a 
temperature of 15.5° C. is unfavorable 
for germination, and that below that 
point germination fails. Delacroix 
(1903 a: 139) states that mature spores 
germinate after forty-eight hours 
at a temperature of about 16° C. 
(6o.S°F.). 

ASCOSPORE GERMINATION (Fig. 30). 

The ascospores germinate readily in 
tap water and potato agar. The time 
required for the process is from six to 
twelve hours. In some cases a septum 
is developed in the ascospore during 
germination. 

incubation period. The period of 
incubation on apple bark, as stated by 
Potebnia (1907:16), is about four 
days. On foliage it is about five 

days, according to the observations of Scott and Rorer (1908:50-51). 

Inoculations made by the writer on bark show that the time between 




Fig. 30. 



stages in the germination 
of ascospores 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits iog 

inoculation and the first sign of the disease is from two to seven days, 
varying with the strains of the fungus used and the meteorological con- 
ditions. The average is four days. On fruit, discoloration appears after 
from twenty-four to forty-eight hours. 

pathological histology. Fruit. — If a section of an apple fruit is 
made perpendicular to the surface, the cuticle, epidermis, hypodermis, 
cortex, and scattered vascular bundles are in evidence. The epidermis 
is composed of a single layer of rectangular cells, the outer walls of 
which are strongly thickened by a waxy infiltration to form the cuticle. 
Immediately below the epidermal cells is the hypodermal parenchyma, 
the cells of which are distinctly different from those more deeply 
seated. They are compactly arranged, comparatively small, and oblong, 
with the greater diameter parallel to the surface. They contain the 
coloring matter of the fruit. There is a gradual transition from these 
cells to the large isodiametric cells that make up the mass of the apple 
tissue. The veinlets come from ten main veins and by continued 
branching the bundles become scattered, being finally lost in the 
cortex. 

There is a sharp line of demarcation between the healthy and the 
diseased tissues (Plate xn, 2); this is especially noticeable in the hypo- 
dermal parenchyma. The coloring matter is abundant in the normal cells 
of the hypodermis ; at the junction of the two regions the coloration is lost 
very abruptly and the tissue is a distinct brown. All the affected region 
is brown and the discoloration in the cortex extends beyond that in the 
hypodermis. Apparently the hypodermis is attacked along the advancing 
margin of the lesion from the cortex below. The mycelium of the fungus 
is found in advance of any apparent change in the normal color, and is 
found in the cortex first, at a point several cells in advance of the affected 
hypodermal cells. The hypodermis appears to be undermined. The walls 
of the cells in this region are greatly thickened; the process is apparent 
within a week after infection, and when the apple becomes mummified 
the lumen of the cell is nearly closed. Dandeno (1906) states that there 
is a production of cellulose in the cell wall of the apple in the course of 
its decomposition. Starch is also produced in the cells invaded by the 
mycelium of the fungus, but with the thickening the starch grains dis- 
appear. The excessive thickening is regarded by Dandeno as resulting 
in the preservation of the mummy. 

The mycelium is usually, if not always, intercellular. In thick, free- 
hand sections strands may be found crossing the cell cavity, but cell-wall 
penetration has not been observed. Frequently small threads appear 
to pass into the cell of the host from the parent branch which is in the 
intercellular space, but no opening in the host-cell wall has been seen. 



no 



Bulletin 379 




Such hyphas are regarded as being intercellular, merely giving the appear- 
ance of an intracellular habit because of the thickness of the section; 

in thin, microtomed sections 

the threads are found be- 
tween the cells. In certain 
cases the hyphre appear to 
be within the cells, but one 
may mistake a large intercel- 
lular space for a cell lumen. 
Dandeno (1906) states that 
the mycelium is intercellular, 
but that small threads enter 
the cells and even pass 
through them (Fig. 31). 

Leaves. — The lesion pro- 
duced on the leaf is largely 
necrotic. The cells are 
brown, collapsed, and ob- 
viously dead. The average 
thickness of 'the normal 
apple leaf is about 142 (i, 
whereas that of the diseased 
area is about 61 n (Fig. 32). 
The epidermal cells of the affected tissue are flattened and bear little 
resemblance to normal epidermis. The palisade cells maintain their 
relative position but are considerably shortened. The cells of the spongy 
parenchyma are shriveled and irregular in form (Fig. 32). 

In some cases the lesions are limited by a vein, and, although a small vein 
may mark the extent of the 
diseased area, the larger veins 
more frequently act in this 
capacity. In cases in which 
the edge of the spot does not 
fall at a vein, a plate of cells 
surrounds the lesion and limits, 
for a time at least, the extent 
of the fungus. 

The structure of the leaf at 
the margin of a spot is very 
different from either the 
healthy or the dead parts. The process of differentiation apparently takes 
place in considerable advance of the fungus. In some stained sections 



HISTOLOGICAL CH \NGES IN THE FRUIT OF 
APPLE 

Showing appearance of healthy tissue at left and diseased 
tissue at right, and the mycelial relationship to the host cells 




Fig. 



HISTOLOGICAL CHANGES 
LEAF TISSUE 



IN DISEASED 



Showing healthy and diseased tissue. The beginning of 
the subenzed layer, represented by heavy-walled cells in a 
line from epidermis to epidermis, should be noted 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits hi 



a row of cells with dark-stained walls is seen in the leaf (Fig. 32). 
They are arranged in a direct line from the upper to the lower epi- 
dermis. This involves the palisade cells and the spongy parenchyma, 
the latter tissue now being composed of more densely packed, but large, 
cells. With the advance of the fungus this layer increases in size and 
number of cells until the diameter is increased over that of the normal 
part. An additional layer of palisade cells may be developed in this 
region, but in a late stage the entire mesophyll becomes densely filled 
with large, irregularly shaped cells. The elongated palisade cells are 
completely changed and become isodiametric in form. The apparent 
stimulation results in hyperplasia and metaplasia of the palisade cells 
and in hyperplasia of the spongy tissue (Fig. 33). 

The diseased cells give a test for suberin with chlor-iodide of zinc and 
with cyanine-glycerin. Certain stages in the development of the leaf spot 
show discoloration of the epi- 
dermal cells up to the suber- 
ized layer only. Later, how- 
ever, the epidermal cells are 
affected beyond this region, 
as evidenced by their loss of 
normal size and color. It ap- 
pears that penetration of the 
temporary layer is accom- 
plished by the fungus invading 
the epidermal cells and thence 
advancing into the healthy 
tissue. At any rate the my- 
celium is found in the epidermal cells in this region. The alternate pro- 
cesses of the formation of this layer of tissue, and the subsequent invasion 
of the tissue beyond the suberized layer by the parasite, give rise to the 
concentric rings previously described. 

Bark. — The tissues of the normal apple stem represent the condition 
found in a typical dicotyledonous plant. In the center is the pith, 
radiating from which region are alternate medullary rays and fibrovascular 
bundles. Outside these is a cylinder of secondary cortex, which is in 
turn surrounded by a cylinder of thick-walled cortex (probably primary 
in nature) and one of cork or periderm. In older stems the epidermis 
is not present. The secondary cortex is composed of several layers of 
phloem, in turn made up of hard, or lignified, sclerenchyma fibers, sieve 
tubes, companion cells, and phloem parencyhma. In a longitudinal sec- 
tion the medullary rays are prominent and are perpendicular to the 
periderm. In the secondary cortex these rays are connected by rows 1 if 




Fig. 33- 



HISTOLOGICAL CHANGES 
1 LEAF TISSUE 



IN DISEASED 



Showing the reactions of the host along the margin of 
thi 1' sion. Metaplasia and hyperplasia are exhibited in the 
mesophyll 



112 



Bulletin 379 



phloem parenchyma which are oriented at right angles "to the direction 
of the medullary rays. These phloem parenchyma cells are rectangular 
and similar to the medullary ray cells; the arrangement of the former 
results in the noticeable stratification of the secondary cortex. 

The material for comparative study of healthy and diseased tissues 
was usually taken so that both areas would appear in the same section. 
Cankers from natural and artificial infection were fixed in Gilson's fixer 




FlG. 34. HISTOLOGICAL CHANGES IN DISEASED WOOD 

Two apple twigs, showing cankers as they appear on surface. The specimens 
on the right are the same twigs, with bark removed to show the streak 

or in chrom-acetic acid, hardened in the usual manner, and finally imbedded 
in either celloidin or collodion. Sections made from such material, as 
well as from fresh tissue, were cut with a desk microtome and stained 
with the following stains: safranine and methyl blue; safranine and 
methyl green; phloroglucin ; and a chlorophyll solution. 

In the normal tissues the lignified and suberized tissues — that is, 
cork and hard sclerenchyma fibers — are stained red with safranin, whereas 






Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 113 



the cellulose tissues, cortical and medullary, are colored blue with methyl- 
blue and unstained with methyl-green. The woody parts stain red with 
phloroglucin. In the diseased part there is a very prominent general 
brownish deposit, located chiefly in the medullary ray cells, the thick-walled 
cortical parenchyma, and the phloem parenchyma. Such cells are not 
stained by any of the stains used. The sclerenchyma fibers and the cork 
are colored red by saf- 
ranine, whereas suberized 
cork cells are made 
green with a chlorophyll 
solution. Diseased wood 
shows a test for lignin 
phloroglucin. 

The more striking ex- 
ternal symptoms of the 
canker noted are the dis- 
coloration of the bark, a 
crevice at the margin of 
the lesion, and a sinking 
of the tissues. It has been 
noted elsewhere that the 
organism penetrates the 
wood to a limited extent 
only, so that the more 
notable changes occur in 
the bark. The canker is 
sometimes superficial, the 
attacks of the organism 
being confined to the cor- 
tical tissues. Attacks on 
the wood of old limbs are 
not frequent, but on twigs 
the wood is subject to 
common invasion by the 
parasite. In cross and lon- 
gitudinal sections the first and the second, and sometimes the third, 
layers of wood, and even the pith, are discolored. Closer examination 
shows the mycelium to be very abundant within the vessels of the xylem 
and in the woody parenchyma. In this region the characteristic brown 
deposit is found, but is located chiefly in the cells of the medullary 
rays and the wood parenchyma. Inoculations on young apple trees in 
the greenhouse with the ascospore strain (no. 82, from apple) show that 




FlG. 35. HISTOLOGICAL CHANGES IN DISEASED WOOD 

Cross section of part of apple twig, showing brown deposit in 
wood fibers and wood parenchyma cells. Mycelium is also shown 
in the xylem ducts, but it should be noted that none is found 
in other woody elements 



114 



Bulletin 379 



there is a streak developed in the outer layers of wood (Fig. 34), just as 
in the twig blight on chestnut oak, Quercus prinus, as reported by Ingram 
(19 1 2) and noted subsequently by Rankin (1914). The streak is due to 
the discoloration of the ceils, not to the presence of the mycelium 
(Figs. 35 and 36). One has only to examine longisections through the 
streak to be convinced that the hyphal threads do not grow in strands 
and are not otherwise arranged so as to give such an appearance to the 
tissue. 

In the case of the more superficial cankers the ingress of the fungus is 
cut off from the healthy tissue by the development of a cork layer (Fig. 37). 
Such lesions reveal in section the presence of a layer approximating the 
normal periderm, with which it is continuous and which reacts the same 

with safranine and with a chloro- 
phyll solution. These cells in their 
final state are suberized. 

The layer originates by the di- 
vision of cells of the cortical paren- 
chyma. The sclerenchyma fibers 
are not changed. If the layer 
comes in contact with a group of 
sclerenchyma fibers it is inter 
rupted. The more recently affectec 
cells — that is, those nearest the 
margin of the lesion — show a red- 
dish tinge with safranine, indi- 
cating slight suberization through- 
out the region. Later, evidence 
of the cork layer is found just 
beyond the infected zone. Walls 
are laid down to form rectangular cells characteristic of the final 
cork 'layer and of the normal periderm. At this time they do not take 
the safranine, indicating that suberization has not begun. Such sections 
stained with chlorophyll solution also show no suberin reaction. 

A later examination of the marginal layer between healthy and diseased 
tissue stained with safranine will reveal three distinct and characteristic 
zones, as follows (enumerating entad) : a red layer of three or four suberized 
cork cells; a colorless layer of about two non-suberized cells, rectangular; 
and a third layer of about two smaller cells of the same shape bearing a 
brownish deposit, making a distinct brown line. Many slides show the 
reverse relation with respect to the suberized and cellulose layers; the 
colorless layer, composed of cells with cellulose walls, may lie next to the 
diseased tissue, and the cells with suberized walls next to the brown line. 




Fig. 36. 



HISTOLOGICAL CHANGES 
DISEASED WOOD 



Longisection of a part of apple twig, showing 
brown deposit in woody elements. Mycelium is 
again to be seen in the sylem ducts 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 115 



This raises the question as to which cells arc suberized first. The assump- 
tion is that those cells nearest the diseased zone are suberized first. This 
would be expected, in such a case, where response to injury is made by the 
host. But this scarcely explains the cases in which the colorless layer 
borders the affected tissue. In these cases, however, the brown line 
is not so distinct as described above, and often is not in evidence; so that 
this may stand as a younger stage in the formation of the cork layer. 
The cells of the suberized layers do not react alike when stained with 
safranine. A row of cells in the center is the darkest, the color shading 
off on both sides, perhaps 

indicating the amount of fe^^^J/f^s^^ a 

suberi-zation . 

The majority of the cells 
of the layer are densely 
granular, are thin-walled 
at first, and possess large 
nuclei. These have the 
characteristics of rapidly 
dividing cells. 

A section through a 
canker having a crevice at 
its margin shows that the 
break follows the brown 
line. The dead tissues on 
the one hand shrink, while 
the living, normal part in- 
creases in diameter by 
growth, exerting tension on 
all tissues of the bark, and 
the break results. It ap- 
pears that the cells making 
up the brown line are the 
weakest, and thus they mark the line of separation of the diseased 
from the healthy tissue. 

Along the marginal layer diseased pockets occasionally are formed which 
extend into the healthy tissue. Such areas are always in the region of a 
group of sclerenchyma fibers. A cork layer surrounds the pocket. Cross 
sections may be cut so as to include only a portion of one of these pockets, 
making them appear as internal, separate infections. Serial sections, 
however, always reveal their connection with the originally infected tissue. 

In the diseased region are found the same stratified layers as mentioned 
in the survey of the normal secondary cortex. But in the affected areas 




Fig. 



37- 



HISTOLOGICAL CHANGES 
BARK 



IN DISEASED 



Showing brown deposit in the medullary ray cells and 
phloem parenchyma, which cross at right angles resulting in 
a stratified appearance in the phloem. Below the diseased 
region is seen the cork layer 



n6 Bulletin 379 

both the cells of the medullary rays and the phloem parenchyma stand 
out very prominently, being filled with the brownish deposit. The 
remainder of the old phloem elements, the sieve tubes, companion cells, 
and sclerenchyma fibers, are not discolored at all. (Fig. 37.) 

The brown mycelium of the fungus is found very abundantly throughout 
the diseased area. It is intercellular, except when it encounters the xylem 
and the hard sclerenchyma fibers; it is not easy to say just what the 
relationship is with respect to hard sclerenchyma fibers. It is noted else- 
where that the hyphae are found within the tracheal tubes. The threads 
for the most part pass up and down the stem. This is in accordance with 
the external symptoms of a lesion. It has been stated previously that 
where the cork layer encounters a group of sclerenchyma fibers it is inter- 
rupted, and the fungus breaks through the barrier as laid down by its 
host. There is no evidence that the suberized cells are ever penetrated. 
Mycelium is found advancing through the layer at points where the 
sclerenchyma fibers cross it, a discoloration precedes the hypha, and 
almost before the threads get into the healthy tissue the latter is changed 
in its normal color. Very soon after is found evidence of a secondary 
cork layer, which usually branches from the primary layer at some point 
beneath the point of secondary penetration. This extends around the 
newly affected region, finally passing above to the normal periderm. 
Repetition of this process, accompanied by the formation of crevices at 
each successive cork layer, results in the concentric lines or cracks so 
characteristic, externally, of the lesion. The drying oiit and death of the 
cells results in their collapse, and the affected part shrinks. 

CONTROL 

BLACK ROT 
EXCLUSION BY LEGISLATION 

As previously noted (Evans, 19 10), the British Government at Cape 
Colony has legislated against black rot. Importers are warned that, 
under a government notice of 1908, all consignments of pomaceous fruits 
found infected with this organism to the extent of one per cent and upward 
will be destroyed on arrival at the Colony or returned to the consignor. 

SPRAYING 

It was suggested by Sturgis (1893 b) that spraying in August and 
September would prevent black rot of quince. The following year the 
same author (1894) found that a 0.03-per-cent solution of copper sulfate 
is fatal to the fungus. More recently Waite (1906:19) recommends the 
same treatment as for apple scab. Wolf (1913) concludes from experi- 
ments conducted in Alabama that bordeaux 4-4-50, applied as follows, 
will be effective: the first spraying, about July 15, when the disease is just 



Black Rot, Leap Spot, and Canker of Pomaceous Fruits 117 

appearing; the second, two weeks later. This schedule gave satisfactory 
control, the sprayed fruits showing less than one per cent diseased on 
certain varieties. Control was less complete on Black Ben Davis, which 
exhibited from ten to fifteen per cent of black rot. Lime-sulfur was found 
to be wholly ineffective under southern conditions in 1912. 

It should be remembered that frequently infections follow the work of 
the codling moth, and, as stated by Clinton and Britton (1910), the 
control of this insect lessens the amount of rot starting at such centers. 
The work heretofore described indicates that certain insects carry the 
spores; it is therefore important to consider the control of these pests. 

HANDLING OF FRUITS 

It is apparent from the life history studies that spores of the black rot 
organism are present in the orchard at picking time and are carried into 
storage. It has also been learned that the fungus effects penetration only 
through injured tissue. Consequently one factor in obtaining apples of 
good keeping quality is the elimination of mechanical and other injuries 
t( 1 the fruit ; the occurrence of black rot in storage is undoubtedly connected 
with the handling methods in use in the orchard. 

t 

STORAGE 

It has been found by Lamson (1902:81), and subsequently by Eustace 
(1908), that the temperature of the storage room should be about 31 
to 34 F. (-0.5° to 1.1 C). Higher temperatures allow growth of the 
fungus. It is important to note that when apples are stored in barrels, 
about one week is required for the temperature of the center of the 
receptacle to become equal to that of the storage room. 

leaf spot 
spraying 

It seems that Alwood (1892) was the first to advocate the use of sprays 
for leaf spot. He recommends two applications, as follows: the first, 
just as the petals have fallen from the apple, using bordeaux mixture 
4-5-50; the second, about twenty to twenty-five days later. The recom- 
mendations of later writers differ in number of applications and in type 
of fungicide. It is very apparent that the number of sprayings in a given 
year will depend on the character of the season. Ordinarily two or 
three applications are necessary, according to Brooks (1909, and 1912, 
a and b) and others. In certain seasons of considerable rainfall additional 
sprayings may be necessary. 

As previously noted, in some districts at least the leaves are infected 
shortly after they unfold from the bud , and infections may continue through- 
out the spring according to Brooks (1909:124). Later Brooks and De- 
Meritt (191 2 : 188) conclude that the period of infection extends throughout 



n8 Bulletin 379 

the middle of the summer. The number of applications then to be made 
will depend on the character of the season and the abundance of spores 
present. 

In some sections of the country where apple scab also is to be combated, 
the regular scab sprayings have been generally recommended as sufficient. 
These are given by Wallace (1913:589-590) as follows: the first, when 
the blossoms show pink; the second, after the blossoms fall; the third, 
two or three weeks later. If later scab sprayings are necessary, the 
leaf spot will be controlled. Scott (1906:33) states that the disease 
may be controlled in connection with the treatment for bitter rot; for 
the latter disease he recommends from four to six applications of bordeaux 
mixture, made at intervals of two weeks beginning about six weeks after 
the trees blossom. 

Apparently bordeaux mixture has been most commonly employed 
for leaf spot. Brooks (191 2 b: 15) maintains that it is the most effective 
fungicide for apple diseases, but points out that an objection to its use 
lies in the fact that spotting of the foliage and russeting of the fruit are 
likely to occur if showers follow its application. The spots produced on 
thfe leaves resemble those caused by the fungus. For leaf spot alone, 
Brooks (page 8 of same reference) finds that self-boiled lime-sulfur best 
holds the disease in check. 

Lime-sulfur is regarded by Brooks (19 12 b) as a satisfactory substitute 
for bordeaux, and in a later publication Brooks and DeMeritt (1912) 
show that commercial lime-sulfur at a strength of one gallon to twenty-five 
gallons of water reduced the infection from about 95 per cent to 26 per cent. 
When used at a strength of one gallon to fifty gallons of water, the lime- 
sulfur was found to be less effective. Brooks considers this fungicide 
about as efficient as bordeaux, and, because of the injury from the latter, 
lime-sulfur would appear the more desirable. 

CULTIVATION 

Brooks and DeMeritt (19 12) have observed marked contrast between 

the amount of infection in sod and in cultivated orchards. They record 

the former as showing 0.79 spot per leaf, whereas in the latter there was 

only 0.47 spot per leaf. They say (page 189 of reference cited): 

The trees hail been treated alike in every other respect and were of equal vigor when 
the experimental work was begun ; it was, therefore, evident that cultivation had reduced 
the disease almost one-half. This reduct ion was probably partly due to the fact that the 
leaves were plowed under on the cultivated plots, but the lack of general vigor in the 
trees on the sod plots was apparently partly responsible for the difference. 

CANKER 

HISTORICAL AND INTRODUCTORY 

The control of cankers has been a matter of consideration for some time. 
Nearly three centuries ago Parkinson (1629:550) recommended surgical 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 119 

methods together with a wound dressing of vinegar. Similar advice is 
given by Harrison (1823:342), who suggests a dressmg of soot, water, 
and train oil. He recommends drainage of the soil in severe cases. 

In more recent times, beginning with the appearance of the work of 
Paddock (1899 b), the recommendations are all essentially of the same 
nature. The employment of the common methods of orchard manage- 
ment — cultivation, fertilization, pruning, and spraying — is recom- 
mended, in order to promote general vigor. Keeping the trees in good 
growing condition is claimed to be essential (Warren and McCourt, 1905). 
Spraying to protect the bark is frequently recommended (Bethune, 1909 : 30, 
and others), while scraping the bark and applying a wash is suggested 
by Paddock (1899 b: 190) and others. Pruning of diseased limbs and 
the growing of a new top is being practiced by some growers. 

The control measure's more commonly employed by the growers of 
New York State are pruning and spraying; other measures, as determined 
by circular letters and personal observation, are surgery, cultivation, 
fertilization, and mulching. The success of these methods varies and 
seems to depend on the vigilance with which the grower pursues the 
disease. 

surgical methods 

pruning. In pruning for the control of canker, two methods may 
be employed: the limb may be cut from the tree entirely, or the cankered 
bark may be removed. In either case a wound will result and the appli- 
cation of a dressing becomes essential. 

Removal of limbs. — The question frequently arises, when shall only 
the canker be cut out, and when is it necessary to remove the limb? No 
general rule can be laid down, but each case must be examined carefully 
and procedure taken accordingly. If the limb is large and productive, 
its removal should be postponed. This is commonly the practice. But 
to wait until the limb is not producing satisfactorily usually means that 
the canker will aid in bringing the branch to destruction. In such cases 
it is advisable to prevent the loss by eradicating the cankered spot by 
surgery. 

If the limb is not producing, whether large or small, its removal for 
the purpose of eliminating the fungus is the alternative. The cut should 
be made so that another limb, or water sprout, may be allowed to grow 
in the approximate space left by the part removed. This method of 
treating the New York apple tree canker is employed in certain orchards 
along the Lake Ontario belt in this State. One grower is very successful 
in this measure of control. This, with protection from new infections 
by careful spraying of the entire tree — trunk and limbs — renders even 
the highly susceptible Twenty Ounce variety practically free from canker. 



120 Bulletin 379 

Grafting of stubs left by the pruning of the affected parts of limbs 
is occasionally practiced. This may be justified in certain cases, although 
as a rule it should be supplemented in the main by the method just 
described. 

Removal of diseased bark. — The cutting out of cankers is a method 
to be employed when the grower is satisfied that the value of the limb 
warrants it. An attempt to remove all kinds and sizes of cankers from an 
infested orchard without regard to such a consideration is likely to result 
in the discouragement of the orchardist with the whole undertaking. 
The equipment necessary for use in the removal of cankered bark consists 
of a drawshave and a farrier's knife. The limits of the diseased area are 
ordinarily determined by making an external examination of the canker. 
Where this method is not reliable, small bits of the outer bark may be 
removed, following the line of the discoloration until the limits are deter- 
mined. Similarly the depth of the canker is defined. 

The shape of the cut will vary somewhat with that of the canker to be 
removed. So far as possible, the wound when finally finished should be 
lenticular in form. This will facilitate callus formation. If the wound is 
rectangular the upper and lower edges heal more slowly. The edge of 
the wound should be perpendicular to the long axis of the limb, for cuts 
made at a slant will result in a certain amount of dead cortex, which is 
undesirable from the standpoint of new infections. A possible exception 
to this method of trimming the margin is to be found at the lower end 
of the wound. Here the edge should be slanting enough to permit 
drainage of moisture. 

wound treatment. It is frequently advised that the wound should 
be disinfected and protected. The latter is certainly commendable 
practice, but whether the former is necessary will depend on the nature 
of the wound dressing. 

Wound disinfection. — If the dressing itself is a disinfectant, a special 
disinfectant will not be necessary. In case one is needed, mercuric 
chloride at the usual strength (1-1000), or copper sulfate (1 ounce to 1 
gallon of water), is most commonly used. 

Wound protection. — The necessity of a protective covering for wounds 
is twofold : to check the weathering of the wound, and to prevent the growth 
of bacteria and fungi. It follows, then, that the fundamental requirement 
of a wound dressing is that it should be a preservative and a pre- 
ventive. Briefly, then, the dressing should have antiseptic qualities, and 
should be fluid, reasonably inexpensive, and easily prepared and applied; 
it is essential that it should give complete covering; it must be impervious 
to air and water, must be durable, and must not injure nor kill the 
tissues nor interfere with the healing process. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 121 

The preparations now most commonly used are paint, tars, and 
asphaltum. In some cases commercial tree paints are employed. It is gen- 
erally agreed that paints are an inefficient covering, whereas asphaltum 
once applied gives the desired protection. Asphaltum, however, is more 
difficult to apply. This is particularly true if the asphaltum used is 
rendered liquid by heat ; if it is dissolved in gasoline it is more easily pre- 
pared and hence more available. The combination of asphaltum and 
gasoline has been applied rather extensively in the orchard of Fred Hazle- 
ton, at Leroy, New York, and from all appearances is commendable. 

The writer has used coal tar for the past three years with good success. 
This is a residual tar derived in the manufacture of artificial gas from coal. 
According to Lunge (1909), tars may vary even from the same materials, 
depending on the temperature used in the distillation, the shape of the 
retort, and other factors. The use of coal tar as a wound dressing has 
been recommended to growers of the State, and some have complained of 
injury to the healthy tissue from its use while others report it as an appro- 
priate material. Many cases of injury have been found to have resulted 
from the use of creosote, but not from coal tar. The primer must dis- 
tinguish between the two materials. The writer has never seen any cases 
of injury from coal tar on apple trees, and it has been used successfully 
on peaches by Jehle (1913). It is interesting to note a quotation from 
Des Cars as given by Bailey (1907 : 1 1 1-1 13) : 

The application of coal tar should not be made except with considerable caution 
in the treatment of wounds on drupaceous fruits (cherries, peaches, plums, etc.), and 
especially on the plum tree. It has often been observed that the bark of fruit trees 
of this class has suffered from the application of coal tar. This is not the case, however, 
with pome-bearing trees (apples, pears, etc.); to these coal tar may be applied with 
perfect, safety. 

Card (1897 :g) reports experiments in pruning in which he tested various 
materials for protecting wounds. He says of coal tar: " Coal tar, how- 
ever, seems to have been a positive hindrance to the healing process, not 
one wound having been reported as healing extremely well, while the 
majority are reported as healing only fairly well." As a comment on this 
remark, Bailey (1907 : 1 13) says: " It is not said, however, whether the tar 
injured the tissues, or whether the apparent results may not have been 
due to the position and character of the wound quite as much as to the 
dressing. In my own experiments .... tar did no damage." 

In view of the complaints made of injury from the use of coal tar, it 
occurred to the writer that this substance varied sufficiently in different 
parts of the State to account for the injury, if any ever occurred. Samples 
were obtained from the gas plants in the following cities in New York: 
Syracuse, Owego, Batavia, Rochester, Ithaca, Lockport, Buffalo, Albion, 
and Geneva. These samples were applied to wounds of mature apple 



122 Bulletin 379 

trees on the farm of Dr. Johnson,, at Leroy, New York, in "August, 1912. 
Examination at intervals during the growing seasons of 1912 and 1913 
showed equally good healing and no injury. Another orchard, near 
Batavia, New York, owned by Chapin & Son, has been extensively treated 
with coal tar, with results similar to those just described. The writer has 
applied coal tar to Northern Spy, Baldwin, and Hubbardston apples in 
an orchard at Byron, New York, and no detrimental effects have been 
observed. In some cases the wound has been disinfected by the use of 
mercuric chloride (1-1000), but no difference in the efficiency of protection 
was observed between wounds so treated and those not disinfected. The 
writer feels safe in recommending the use of coal tar without previously 
disinfecting the wounded surface. 

The cost of canker treatment — that is, the removal of diseased bark 
and the application of a dressing — is not an easy matter to determine. 
Where it is done extensively the grower usually does the work along with 
the regular pruning, so that the cost of canker treatment alone can hardly 
be separated from that of the whole operation. In an apple orchard at 
Leroy, New York, careful work was done in 1912 by A. S. Davis. The 
orchard contained 950 forty-years-old trees. The orchard had been 
neglected for several years, and dead limbs, cankers, collar rot, and heart 
rot were abundant. Mr. Davis furnishes the following figures: 

Cost of trimming $407 . 90 

Coal tar, 40 gallons, at 20 cents a gallon 8.00 

Corrosive sublimate • .75 

Applying tar 30 . 00 

Removal and destruction of brush 54 . 70 

Total $501 -35 



The following data are taken from a similar orchard at Batavia, New 
York: 

Miscellaneous data 

Number of trees 360 

Age of trees 30 years 

Cost 

Labor, 348 hours, at 25 cents an hour $87 .00 

Coal tar, 10 gallons, at 15 cents a gallon 1 .50 

Corrosive sublimate • 5° ' 

Total $89.00 



It is seen that the average cost of the work in the Leroy orchard is 
about fifty-two cents a tree. It must be borne in mind that the orchard 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 123 

had not been pruned in several years, which accounts in part for the 
high cost of the work. In the Batavia orchard the average cost is approx- 
imately twenty-five cents a tree. These figures do not represent the cost 
of treating the cankers alone; this process itself would be considerably 
less than either of the above figures. 

wound healing. Woufid cork. — According to Hartig (1894:225), 
whenever the living phellogen is injured a new zone of phellogen, or 
cork, which is continuous with the cork layer along the edge of the wound, 
is formed from the uninjured cells which are situated deeper in the 
cortex. The cortical parenchyma, which lies beneath the periderm, 
possesses sufficient power of cell division to enable it to keep pace with 
the increasing thickness of the stem. But in the case of the wound its 
reproductive capacity is confined to the development of a periderm close 
beneath the surface of the exposed tissues. Its formation does not depend 
on the season of the year, but it may be formed even in winter. 

Wound ivood. — Hartig (1894:228) states that wood exposed by a 
wound has the power of producing new cortex and new wood when the 
cambium is active and when the cambium layer and young wood are 
protected from drought. In such a case, regeneration of the covering 
layers is effected. The cambial region consists of embryonic bast and 
wood, which is capable of growth and ultimately of a certain amount 
of differentiation. The wood thus formed is termed wound wood. 

Callus. — Callus may be developed when the cambium has dried up 
or when it is absent from the surface i >f the wound. Its formation proceeds 
from the edge of the wound, beginning in the cambium. Hartig (1894: 
231) states that it is a purely mechanical process and results from the 
reduction of the bark pressure on these tissues. There is always a certain 
amount of tension in the cortical mantle, whereby a considerable pressure 
is exerted on the cambium. Should this pressure be locally reduced by 
a wound's reaching the wood, the processes of cell division and growth 
are accelerated not only along the edges of the wound but also at greater 
distances. The callus cushions advance from the edges of the wound, 
finally coming in contact and coalescing. This coalescence is retarded 
if the callus is clothed at an early stage with dead bark. 

It has been noted that wounds made in cutting out cankers should be 
pointed in order to permit rapid healing. In this connection Hartig 
(1894:232) states that the formation of callus proceeds mure vigorously 
in case of a longitudinal incision than when the incision is transverse. 
This is explained by the nature of the pressure by the bark in consequence 
of peripheral enlargement of the stem. The pressure here acts like that 
of a barrel hoop on the staves, and so callus develops more rapidly along 
the lateral margins of the wound. In this connection the question of 



124 Bulletin 379 

slitting the lower edge of the callus arises. Reasoning from the data 
regarding the development of the callus, it seems advisable to practice 
this operation each year; this prevents the callus from bunching, and 
stimulates it to more ready occlusion of the wound. 

SPRAYING 

The effectiveness of spraying for canker is a question frequently raised. 
It is the belief of the writer that spraying as a preventive, but not as 
a cure, is worthy of attention. It is true, however, that growers report 
cases of curing canker by spraying. The fungus mycelium is protected 
by the bark ; hence sprays will not reach it, and eradication of the fungus 
from a given lesion by spraying seems highly impossible. Spraying to 
protect healthy bark from infections would certainly appear advisable, 
but the data at hand are somewhat conflicting. The writer recalls an 
orchard in which canker does not occur. The trees are sprayed carefully 
each year, according to general recommendations for apples. Some of 
the trees are Twenty Ounce, but they are free from the disease. The 
limbs are kept coated with spray throughout the summer, and as late 
as the middle of August these trees are still covered. In contrast to this 
orchard, another is recalled which is severely affected with canker, yet 
the trees are given the regular sprayings. The difference in these cases 
may be accounted for by the lack of thoroughness of the spraying in 
the second orchard. Since protection is the principle involved in this 
method of control of canker, the success of any attempts in this direction 
is determined by the completeness of the covering. 

GENERAL CONSIDERATIONS 

The destruction of rubbish about the orchard is no new suggestion. 
Peck (1879 : 2 1) recommends that affected fruit should be removed from the 
orchard and destroyed. The destruction of fallen leaves is recommended 
by Alwood (1892). Sheldon (1905) and others suggest picking rotted 
fruit before the fungus spores mature in the case of quince black rot; 
Sheldon adds that this might not be possible with apples because of the 
size of the trees. In Alabama, however, Wolf (1913), as has been previously 
noted, controlled the disease by spraying. The opinion is held by Brooks 
and DeMeritt (1912:189) that affected leaves should be plowed under, 
while clean cultivation is the recommendation of Reed, Cooley, and 
Rogers (1912:5). The removal and burning of affected limbs is advocated 
by Bethune (1909:30) and others. 

The ability of the fungus to pass from one part of the apple tree to 
another only adds to the sources of inoculum, so that sanitary measures 
become of special importance. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 125 

orchard management 

The value of careful handling of fruit to prevent injury has been 
emphasized. This is based on the principle that the causal organism 
is a wound parasite. The same care should be exercised with reference 
to the bark of the tree; injury should be avoided whenever possible. 
Injuries to bark are likely to result from cultivating implements and 
harness, the careless handling of ladders while picking, and climbing 
over the trees with rough-soled boots. The importance of guarding against 
such orchard practice lies in the fact that cankers begin in just this sort 
of place. 

It has been mentioned that the fungus follows winter injury. As 
a protection against winter injury, Reddick (1912:37) advocates early 
plowing in the spring, and cultivation to give the trees the advantage 
of conserved moisture; he recommends that cultivation should cease not 
later than August 1, in order to start the trees into maturation. Cover 
crops, to take up excess moisture in the autumn, should be sown. Soil 
drainage in low ground, and a good circulation of air, are important 
considerations. 

When it is desired to grow varieties that are susceptible, the canker 
difficulty may be obviated to a considerable extent by working over the 
larger limbs of more resistant varieties to the one desired. This has 
been done with apparent success in a few instances. The difficulties 
involved are that pruning must be done every year to remove all sprouts 
from the stocks, and that renewal of old branches cannot be effected 
so readily. Such a treatment also throws the bearing area higher into 
the air, so that in the case of erect growers, such as Twenty Ounce, thorough 
orchard operations are made more difficult. 

RESISTANT VARIETIES 

Since certain varieties of the apple — for example, Esopus and Twenty 
Ounce — are more susceptible to canker than are other varieties, the 
growing of other varieties will undoubtedly render the problem of control 
less difficult. Twenty Ounce, however, is one of the most satisfactory 
fall varieties for commercial planting in New York State. The question 
therefore arises, whether the orchardist should sacrifice the growing of this 
variety in the hope of escaping the problem of canker control. The 
evidence at hand indicates that if a grower wishes to raise Twenty Ounce, 
his success in keeping the trees free from canker will depend on his efforts. 
Observations warrant this opinion. It is true that, as stated by Warren 
and McCourt (1903), "something more than thrifty growth seems to be 
necessary in order to prevent the destruction of the Twenty Ounce"; 
so that vigor in itself should not be given too much dependence. Well- 



126 Bulletin 379 

cared-for trees of this variety are often severely cankered. It is assumed 
that the trees must be in a thrifty condition in order to give the best 
results, but the control problem does not end here, for vigor does not estab- 
lish nor maintain resistance. 

AN ENEMY OF THE PATHOGENE 

Potebnia (191 2) 8 reports an interesting case of a fungus, Helico- 
myces Sphaeropsidis Potebnia, living as a parasite within the conidia of 
Sphaeropsis pseudodiplodia [- Physalospora Cydoniae]. Infection takes 
place when the host (the conidia of Physalospora Cydoniae) is in the Macro- 
phoma stage. He notes a similar case reported by Japp, in which Hcli- 
comyces niveus Bres. & Japp is parasitic on Diplodia inquinans West., 
and states that in Japp's herbarium specimen all pycnospores in the 
infected pycnidia were killed by this parasite. 

BIBLIOGRAPHY 
(Anonymous) 

1899 a The app'e canker. Country gent. 64:88. 

Briefly summarizes the works of Waite and Paddock. 

1899 b The apple canker. Country gent. 64:208. Illustrated. 

The illustration is a text figure, and the author contends that it is the first figure of 
the disease published. 

1899 c Perhaps apple canker. Country gent. 64:248. 

A reply t~> an inquiry concerning the apple injury which is regarded as caused by Sphae- 
ropsis Malorum. Remedy suggested. 

Alderman, W. H., Giddings, N. J., and Rumsey, W. E. 

1913 Orchard spraying. West Virginia Univ. Agr. Exp. Sta. Circ. 7: 
1-4S, fig. 1-33. 

Mention black rot. leaf spot, and canker, and suggest control measures. 

Alwood, W. B. 

1892 Brown spot. In Four diseases of the apple, and treatment of 

same. Virginia Agr. and Mech. Coll. Agr. Exp. Sta. Bui. 
17:59, 62. 

Describes a leaf disease and uses the name brown spot. Notes three successive out- 
breaks in a summer. Questions whether Phylloslicta pirina is the cause. 

1893 Injurious insects and diseases of plants with remedial measures 

for the same. Virginia Agr. and Mech. Coll. Agr. Exp. Sta. 
Bui. 24:1-40. Illustrated. 

The apple orchards of Virginia said (p. 24) to suffer chiefly from two foliage diseases 
one of which is called brown spot, attributed to the attacks of Phylloslicta pinna. 

1898 a The leaf-spot disease of apple, Phyllosticta pirina Sacc, and 
several unrelated forms occurring therewith. Amer. Assoc. 
Adv. Sci. Proc. 47:413. 

Records the foil i occurring with Phyllosticta pirina Sacc: Sphaeropsis 

Malorum Peck, Hendersonia Malt, and an undetermined species. 

8 Translated by C. D. Sherbakoff. formerly of the Department of Plant Pathology at Cornell University. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 127 

1898 b On the occurrence of a yeast form in the life cycle of the black 
rot of apple, Sphaeropsis Malorum Peck. Amer. Assoc. Adv. 
Sci. Proc. 47: 422. 

Records the discovery of a yeast form occurring in cultures of this fungus, which 
cm isolation and reinfection on the fruit of apple produced the common fruiting 
bodies of Sphaeropsis Malorum, 

1902 Orchard studies. — XV. The bitter rot of apples. Virginia Agr. 
Exp. Sta. Bui. 142:250-274, pi. 1-4. 

States (p. 257) that Sphaeropsis Malorum Berk, invades fruit already decaying from the 
attacks of the bitter rot fungus. 

Alwood, W. B., and Price, H. L. 

1902 Orchard studies. — V. Report on crab apples. Virginia Agr. 
Exp. Sta. Bui. 132:3-14, fig. 1-4. 

Note (p. 6) that certain varieties are especially subject to the black rot canker (caused 
by Sphaeropsis Malorum), 

Arnaud, G. 

1912 Notes phytopathologiques. 1. Sphaeropsis pseudodiplocli a. Mont- 
pellier (France) Ecole Nat. dAgr. Ann. 12:5-17, fig. 1-5. 

Discusses the fungus as it occurs on several different plants. Notes the variable 
morphology of the organism and reports the discovery of an ascomycete associated 
with the pycnidial form. The ascomycete is named Physalospora Cydoniae and is re- 
garded as probably the perfect stage of Sphaeropsis pseudodiplodia. 

Arthur, J. C. 

1885 Quince rot. In Report of the Botanist. New York (Geneva) 
Agr. Exp. Sta. Ann. rept. 3:372. 

Describes symptoms, and proves the pathogenicity of the fungus (which he calls Sphae- 
ropsis Cydoniae C. & E.) on quince fruit. 

Baccarini, P. 

1890 Note patologiche. Ital. nuovo giorn. bot. 22:64-70. 

Reports Sphaeropsis Malorum on pears, apples, and peaches in storage. Discusses 
sclerotia and pycnidial development. 

Bailey, L. H. 

1907 The healing o r wounds. In The pruning-book, p. 76-132, fig. 
68-110. 

Gives a chapter on the healing of wounds, taking up the nature of wounds, suggestions 
for the pruner, dressings for wounds, making cuts. 

Baldwin, C. H. 

1912 Black rot. In Some important diseases of apple. Indiana State 
Entomologist. Rept. 5:249-252. Illustrated. 

Gives notes on black rot, leaf spot, and canker. 

1914 Black rot (New York apple-tree canker and apple leaf spot). 
In Apple diseases. Indiana State Entomologist. Rept. 7: 
150-152. Illustrated. 

Describes the nature of the injury. 

Bary, A. de 

1887 Comparative morphology and biology of the fungi, Mycetozoa, 
and bacteria, p. 1-525. (Translated by H. E. F. Garnsey 
and I. B. Balfour.) 

Discusses (p. 247) types of pycnidial formation in general. 



128 Bulletin 379 

Beach, S. A. 

19 1 2 Black rot.. In Spraying practice for orchard and garden. Iowa 
Agr. Exp. Sta. 6111.127:50-51. Illustrated. 

Black rot observed to occur on some of the summer and early fall varieties. 

Beach, S. A., Lowe, V. H., and Stewart, F. C. 

1899 Apple tree canker. Also, Leaf spot. In Common diseases and 
insects injurious to fruits. New York (Geneva) Agr. Exp. 
Sta. Bui. 170:382-384. 

Describe canker, caused by Sphaeropsis Malorum Peck, and leaf spot, due to Phyllosticta 
spp., with recommendations for control. 

Beal, W. J. 

1898 Diseases of the apple. Michigan State Hort. Soc. Ann. rept. 
27: 174-183, pi. i-4- 

Discusses (p. 178) symptoms of black rot of apples, and compares it with soft rot (caused 
by Penicillium expansum Link). 

Berkeley, M. J. 

1836 Sphaeria Malorum. /;; Hooker's English flora, p. 257-258. 

Describes the fungus Sphaeria Malorum Berk. 

i860 Sphaeropsis Malorum B. In Outlines of British fungology, p. 
316. 

Changes the generic name of the fungus from Sphaeria to Sphaeropsis. 

Berlese, A. N., and Voglino, P. 

1886 Macrophoma Malorum (Berk.) Berl. & Vogl. Cited in Sac- 
cardo's Syll. Fung. 10:107. 1892. From Veneto-Trentina 
Soc. Atti. 1886:184. 

The authors divide the genus Phoma into Macrophoma and Phoma, the basis being the 
length of the pyenospores; Phoma Malorum (Berk.) Sacc. becoming, as they believe, 
Macrophoma Malorum (Berk.) Berl. & Vogl. 

Bethune, C. J. S. 

1909 Fungus diseases and insect pests. Also, Cankers on apple trees. 

Ontario Agr. Coll. and Exp. Farm. Ann. rept. 34:26-32. 

Reports (p. 2o1 that cankers do great damage along the north shore of Lake Ontario. 
Says (p. 2g) that spores of Sphaeropsis Malorum are carried by the wind. 

1910 Black rot canker (Sphaeropsis Malorum). Ontario Agr. Coll. and 

Exp. Farm. Ann. rept. 35:35-36. 

States that black rot canker apparently can be successfully controlled by pruning out 
dead branches, cutting out cankers, and coating the bark with spray. 

Bommer, E., and Rousseau, M. 

1885 Florule mycologique des environs de BruxeUes, p. 3-353. 

Sphaeropsis Malorum Berk, is listed (p. 257) on fallen apples. 

Brooks, Charles 

1907 Diseases of the apple. In Seventeenth and eighteenth annual 
reports. New Hampshire Coll. Agr. Exp. Sta. Bui. 1 29 : 
267-270, pi. 15. 

Records black rot and cankers due to Sphaeropsis Malorum Berk, as common; records 
leaf spot due to Phyllosticta pirina Sacc. and P. limitata Peck as serious, with little 
or no effect on it from spraying. States that majority of apple limb cankers are 
caused by Sphaeropsis Malorum Berk., and that few of the orchards visited did not 
show the disease, 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 129 

1909 Black rot, canker, and leaf spot. In Some apple diseases. New 
Hampshire Agr. Exp. Sta. Bui. 144:123-126, fig. 20-24. 

Discusses occurrence, symptoms, etiology, and control of black rot. canker, and leaf 
spot. Lists the following fungi as associated with these diseases: Sphaeropsis 
MaloYum, Coniothyrium pirina, Coryneum foliicolum, Alternaria sp., and one of the 
Tuberculariae. 

1912 a Black rot, canker, and leaf spot. In Some apple diseases and 
their treatment. New Hampshire Agr. Exp. Sta. Bui. 
157:17-20, fig. 20-24. 

Maintains that black rot does considerable damage in storage. Outlines sprayings 
which are said to be fairly effective for leaf spot. 

1912 b Fungicides in the apple orchard. New Hampshire Agr. Exp. 
Sta. Bui. 161 : 1-15. 

Compares different fungicides for control of leaf spot. 

Brooks, Charles, and DeMeritt, Margaret 

1912 Apple leaf spot. Phytopath. 2:181-190, pi. 17, fig. 1-6. 

Give an account of the etiology of leaf spot, paying particular attention to the morpho- 
logical and biological variations in Sphaeropsis Malorum. Infection shown to occur 
from the time the leaves unfold until the last of August. Cultivation, spraying, and 
the removal of cankers given as the important control measures. 

Brooks, Charles, Fisher, D. F., and Cooley, J. S. 

1914 Apple rots. Phytopath. 4:403. (Abstract.) 

List several species of fungi, including Sphaeropsis Malorum, which were isolated from 
market and storage apples. 

Bryce, P. I. 

191 5 Apple leaf -spot or black rot canker. Quebec Soc. Prot. Plants 

from Ins. and Fung. Dis. Ann, rept. 7:86-90. Illustrated. 

Gives an account of symptoms, varietal susceptibility, and control of the disease. 

Bubak, Fr. 

1909 Ein kleiner Beitrag zur Pilzflora von Niederosterreich. Ann. 
myc. 7:59-62. 

Sphaeropsis Mali (West.) Sacc. listed (p. 62) as collected on Pirus Malus in " Hohe 
Warte" bei Wien. 

Burrill, T. J. 

1907 Bitter rot of apples: botanical investigations. Illinois Univ. 
Agr. Exp. Sta. Bui. 118:553-608. 

States that Sphaeropsis Malorum is sometimes associated with the bitter rot fungus in 
cankers. The former organism said to follow the latter under Illinois conditions. 

Burrill, T. J., and Blair, J. C. 

1901 Apple fruit-rots. Illinois Univ. Agr. Exp. Sta. Circ. 37: (12 
pages, unnumbered). Illustrated. 

Special attention given to symptoms of black rot. caused by Sphaeropsis Malorum. Sug- 
gestion that another species causes canker. Discussion on second and third pages. 

Butler, O. 

191 2 Report of the Department of Botany. In Twenty-third and 
twenty-fourth reports. New Hampshire Agr. Exp. Sta. Bui. 
163 : 16-17. 

Mentions the work of Brooks, which appeared later in Phytopathology 2 :i8i-i90 and 
was published jointly by Brooks and DeMeritt. 



130 Bulletin 379 

Caesar, L. 

1909 Black rot canker of apple trees. In Lime-sulphur wash. Part 
II. — Practical and popular treatment. Ontario Agr. Dept. 
Bui. 177:59-61, fig. 16. 

States that on leaves and fruit the disease is seldom serious, but cankers often do great 
damage especially in Prince Edward County. Ontario. 

191 2 Black rot canker. In Our most troublesome orchard insects 

and diseases. Ontario Fruit Growers' Assoc. Ann. rept. 
44:22, fig. 15. 

Author is convinced that the fungus follows winter injury. 

Card, F. W. 

1897 Notes on pinning. Nebraska Agr. Exp. Sta. Bui. 50: 1-10. 

Concludes from experiments that lead paint is the best material for covering wounds; 
grafting wax said to be the next best; coal tar found to prevent checking, but seemed 

to hinder the healing process; pine tar and shellac reported as unsatisfactory. 

Chase, W. W. 

1913 Apple leaf spot. In Principal insects and diseases of the apple 

in Georgia. Georgia State Bd. Ent. Bui. 38:40-41, pi. 6, 
fig. 2. 

Leaf spot caused by Sphaeropsis Malorum said to be one of the most destructive apple 
foliage diseases in Georgia. 

Chester, F. D. 

1901 a Canker in apple and pear. In Pear blight and pear canker. 
Delaware Coll. Agr. Exp. Sta. Bui. 52:6-8, fig. 4-7. 

States that twigs and branches bearing pycnidia of Sphaeropsis Malorum Peck 
are sources of infection. 

1901 b Canker in the apple and pear. In Report of the Mycologist. 

Delaware Coll. Agr. Exp. Sta. Ann. rept. 12: 43-46, fig. 4-7. 

(Same as 1901 a.) 

1902 Pear canker treatment. Also, Canker in apples. In Sundry 

notes on plant diseases. Delaware Coll. Agr. Exp. Sta. 
Bui. 57:8-11, fig. 5-6. 

Describes symptoms and control of canker of pear and apple caused by Sphaeropsis 
Malorum. 

Clement, F. M. 

1913 Winter injury in orchards. Quebec Soc. Prot. Plants from Ins. 
and Fung. Dis. Ann. rept. 5:24-26. 

Says that frost wounds are made doubly serious if not treated to prevent the admission 
of the spores of saprophytic fungi, especially those of the black rot fungus, with the 
consequent development of apple canker. 

Clinton, G. P. 

1902 Black rot, Sphaeropsis Malorum Berk. In Apple rots in Illinois. 
Illinois Univ. Agr. Exp. Sta. Bui. 69:192-193, pi. b, fig. 2. 

Sphaeropsis Malorum Berk, regarded as one of the chief causes of rotting of apples in 
market. 

1904 Black rot, Sphaeropsis Malorum Pk. In Report of the Botanist. 
Connecticut (New Haven) Agr. Exp. Sta. Ann. rept. 27:298, 
342, 352, pi. n, a. 

Black rot regarded as one of the commonest and most universal diseases of the apple. 
Noted also on pear and quince. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 131 

1907 Winter injury and canker, Sphaeropsis Malorum Pk. In Report 
of the Botanist for 1906. Connecticut (New Haven) Agr. 
Exp. Sta. Ann. rept. 30:310-311, pi. 17, a. 

A peculiar limb disease of the apple is doubtfully attributed to winter injury and 
Sphaeropsis Malorum. 

1915 Notes on plant diseases of Connecticut. In Report of the 
Botanist for 1913. Connecticut (New Haven) Agr. Exp. Sta. 
Ann. rept. 38 (1914) : 1-29. Illustrated. 

Black rot noted on stored apples (p. 5). 

Clinton, G. P., and Britton, W. E. 

1910 Black rot, Sphaeropsis Malorum. In Tests of summer sprays on 
apples and peaches in 1910. Connecticut (New Haven) Agr. 
Exp. Sta. Ann rept. 33-34:590, pi. 21, b. 

Authors report occurrence of black rot (due to Sphaeropsis Malorum) on summer and 
stored winter varieties. State that the use of insecticides in keeping out codling 
moth lessens the rot starting from this cause. 

Cook, M. T. 

1913 Report of the Plant Pathologist. New Jersey Agr. Exp. Sta. 

Ann. rept. 33:509-527- 

Black rot of apple and quince, caused by Sphaeropsis Malorum, among the diseases 
listed (p. s 1 2) as most important and most common in the nurseries. 

1914 a Black rot of the apple and quince. In Some diseases of nursery 

stock. New Jersey Agr. Exp. Sta. Circ. 35:13-14, fig. 9. 

Twig and leaf-spot forms of the disease very common in nurseries. It is advised that 
diseased trees should never be set. 

1914 b Black rot (Sphaeropsis Malorum Pk.). In Most common 
diseases of the year. New Jersey Agr. Exp. Sta. Ann. rept. 
34:799, 809. 

Black rot of apples most severe on Red Astrachan, Star, Lawver, Smokehouse. Black 
rot of quince reported as being very abundant and very severe. 

Cooke, M. C. 

1892 Sphaeropsis pomorum (Schwz.). In Sphaeriaceae imperfectae 
cognitae. Grevillea 20:86. 

Suggests that Sphaeropsis pomorum (Schwz.) [= Sphaeria pomorum Schwz.] is probably 
the same as Sphaeropsis Malorum Peck, of which Phoma Malorum Berk., erected by 
Saccardo, is possibly a younger condition. 

Cooper, J. R. 

1913 The control of canker in the orchard. Nebraska hort. 3:2: 1-2. 

Black rot canker is ranked third in importance among cankers in Nebraska. The dis- 
cussion of control measures is directed at the Illinois blister canker. 

Corbett, L. C. 

1900 Brown spot, frog eye. In Fruit diseases and how to treat them. 
West Virginia Agr. Exp. Sta. Bui. 66:202-204, fig. 2. 

Author considers frog-eye. or brown spot (said to be due to Phyltosticta pirina), more 
injurious than either blight or scab. 



132 Bulletin 379 

Crabill, C. H. 

1915 The frog-eye leaf spot of apples. Virginia Agr. Exp. Sta. Bui. 
209:3-16, fig. 1-5. 

Author states that frog-eye leaf spot is the most prevalent of apple foliage diseases in 
Virginia. The annual losses fmm the disease are said to be heavy in that State, but 
systematic spraying has controlled the disease in a satisfactory and effective manner. 
Symptoms are described. Etiological studies are tabulated, and from his experiments 
the author concludes that frog-eye spots are initiated by Sphaeropsis M alarum. All 
other fungi with which he deals are classed as facultative parasites, following 5. 
Malorum, or as pure saprophytes. 

Cummings, M. B. 

1909 Apple orchard survey of Niagara County. Cornell Univ. Agr. 

Exp. Sta. Bui. 262:277-320, fig. 26-40. 

Gives notes (p. 304, table 12) on economic importance of canker. 

Dandeno, J. B. 

1906 A stimulus to the production of cellulose and starch. Michigan 
Acad. Sci. Rept. 8:40-44. 

Claims that the fungus Sphaeropsis Malorum stimulates the cells of ripe apple fruit to 
form starch and to thicken the cellulose walls. Suggests that starch is built up first 
and then dissolved and built into cellulose, the process going on until the fruit is 
mummified and dry, whereupon it is in a state of preservation. 

Delacroix, G. 

1903 a Sur un chancre du pommier produit par le Sphaeropsis Malorum 
Peck. Soc. Myc. France. Bui. 19:132-140. Illustrated. 

Gives an account of the disease which, it is believed, appeared in France at least 
as early as iooi. Discusses the morphology of the parasite and the relationship 
of the mycelium to the tissues of limbs, mentions inoculation experiments, and 
suggests control measures. 

1903 b Sur l'identite reelle Sphaeropsis Malorum Peck. Soc. Myc. 
France. Bui. 19:350-352. 

Reports the examination of the following type material: Sphaeropsis Malorum Peck, 
S. Malorum Berk., Diplodia maura Cooke & Ellis, p. pseudodi plodia Fckl., and 
Botryodi plodia Mali P. Brunaud. Concludes that 5. Malorum, D. maura, and B. 
Mali are all different, and that 5. Malorum in France, S. Malorum Peck, and D. 
pseudodi plodia Fckl. are identical. States that since D. pseudodi plodia was 
described before S. Malorum, the latter name should disappear, and the new com- 
bination S. pseudodi plodia (Fckl.) G. Del. is proposed. 

Dickens, A., and Headlee, T. J. 

191 1 Spraying the apple orchard. Kansas Agr. Exp. Sta. Bui. 
174:251-292, fig. 1-19. 

Give an account of experimental work in the control of black rot by spraying. Bor- 
deaux mixture and lime-sulfur were used on several varieties. 

Douglass, B. W. 

1910 Black rot. In Plant diseases. Indiana State Entomologist. 

Rept. 2 (1908-1909) : 135. 

The disease is briefly described. 

Duggar, B. M. 

1909 Black rot and canker of pomaceous fruits. In Fungous diseases 
of plants, p. 303, 3SO-3S4- %• 169-172. 

A discussion of habitat relations, etiology, and control of the fungus. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 133 

Edgerton, C. W. 

1908 Two little-known Myxosporiums. Ann. rayc. 6:48-53, fig. 1-2. 

Points out similarity and difference between the cankers caused by Sphaeropsis M alarum 
and a new species of Myxosporium, called M. corticolum. The synonymy of 5. 
Malorum is given. 

Ellis, J. B. 

1880 On the variability of Sphaeria Quercuum Schw. Philadelphia 
Acad. Nat. Sci. Proc. 1879:66-70. 

Author would include several enumerated species of Sphaeria. Botryosphaeria, Dothidea. 
and Melogramma under one species, and the name Melogramma fuliginosa is accepted. 
Ascigerous forms accompanied by stylospore forms of the Diplodia or Sphaeropsis 
type. 

Ellis, J. B., and Everhart, B. M. 

1892 The North American Pyrenomycetes, p. 1-703, pi. 1— 41. 

Eustace, H. J. 

1908 Investigations on some fruit diseases. New York (Geneva) Agr. 
Exp. Sta. Bui. 297:29-48, pi. 1-7. 

Shows by experiment that the fungus {Sphaeropsis Malorum) is not destroyed but its 
growth is retarded in storage at temperatures ranging from 2<f to 32° F. Gives results 
of sulfur fumigation in storage. 

Evans, I. B. P. 

1910 The New York apple tree canker or black rot fungus in .South 
Africa. Transvaal agr. journ. 7:62-64, pi. 7. 

Calls attention of South African growers to the presence of "another imported fungus, 
and one which it will not be well to neglect." 

Faurot, F. W. 

1903 Black rot. In Report of fungous diseases occurring on cultivated 
fruits during the season of 1902. Missouri State Fruit Exp. 
Sta. Bui. 6:6-7. 

The name blossom rot is employed for calyx-end infections on apples. Symptoms are 
described. 

1912 Black rot. In Common orchard troubles, spray mixtures, and 
spray calendar. Missouri State Fruit Exp. Sta. Bid. 23: 
14-15, fig. 8-9. 

States that black rot, also called blossnm-end rot. occurs largely on fruits of which the 
skin has been broken, and that owing to the habits of the fungus it is not controlled 
by spraying. 

Floyd, Bayard F. 

1905 Apple canker. Black rot. In Some common fungous diseases 
and their treatment. Missouri State Hort. Soc. Ann. rept. 
48:432. 

Notes that windfall apples are very susceptible. 

Freeman, E. M. 

1905 Black rot of apple (Sphaeropsis Malorum Peck). In Minnesota 
plant diseases, p. 363-364, fig. 194. 

Gives a short general account of black rot, leaf spot, and canker. 



134 Bulletin 379 

Fiickel, L. 

1869 Symbolae mycologicae, p. 1-459, P L I_ 6. 

Descriptions of Diplodia pseudodiplodia Fckl. (p. 393) and Diplodia Malorum Fckl. 
(p. 3Q5). 

Galloway, B. T. 

1892 Report on the experiments made in 1891 in the treatment of 
plant diseases. U. S. Agr. Dept., Veg. Path. Div. Bui. 3: 1- 
76. Illustrated. 

Gives (p. 30) an account of petal and young fruit infection induced by Sphaeropsis 
Malorum. 

Garman, H. 

1895 Spraying experiments in 1895. Kentucky Agr. Exp. Sta. Bui. 
59:111-129. Illustrated. 

Sphaeropsis Malorum said (p. 127) to be the cause of most of the fruit rot in the State. 

1908 Brown rot of apples. In i. Spraying apple trees. 2. Apple 
orchard pests in Kentucky. Kentucky Agr. Exp. Sta. Bui. 
133:8, 65-66. 

The disease on apple fruit (due to Sphaeropsis Malorum) is called brown rot. and spray- 
ing experiments for the control of the disease are reported. 

Giddings, N. J. 

1908 Apple canker. In The occurrence of plant diseases in 1907. 
Vermont Agr. Exp. Sta. Ann. rept. 20:331. 

Apple canker, caused by Sphaeropsis Malorum, said to be rather prevalent in some 
orchards. The statement is made that the disease is easily controlled by pruning 
and spraying, and is thus kept down in most well-tended orchards. 

Green, W. J., Selby, A. D., and Gossard, H. A. 

1915 Spraying program for orchards with combinations recommended. 
Ohio Agr. Exp. Sta. Circ. 149:53-60. 

Suggest (p. 54-55) a combination of insecticide and fungicide for control of codling 
moth, apple scab, and black rot. 

Griffon, E., and Maublanc, A. 

1910 Sur des especes de Sphaeropsis et de Diplodia parasites du 

poirier et du pommier. Soc. Myc. France. Bui. 26:307-316. 
Illustrated. 

Discuss symptoms, and several species of fungi on apple and pear. The conclusion 
is reached that .these trees may be attacked by Sphaeropsis and Diplodia, which act 
as wound parasites. The species involved are regarded as distinct and are briefy 
described; these are Sphaeropsis Malorum Peck, Sphaeropsis pseudodiplodia (Fckl.) 
Del., and an undetermined Diplodia. 

Giissow, H. T. 

191 1 Black rot (Sphaeropsis Malorum Peck.). In Report of the 

Dominion Botanist. Experimental Farms (Canada). Rept. 
1911:246-247. 

Discusses symptoms and control. 



Black Rot, Leaf Spot, and Canker of Pomaceous 'Fruits 135 

Halsted, B. D. 

1892 The black rot of the quince. In Some fungous diseases of the 
quince fruit. New Jersey Agr. Coll. Exp. Sta. Bui. 91:8-10, 
fig- 5-6- 

Concludes from observation and experiment that the species of Sphaeropsis on quince, 
apple, and pear are the same. States that the fungus causes one of the most destruc- 
tive decays of the quince, and that the spores pass through the air or are carried by 
insects. 

1894 Decays of mature apples. In Report of the Botanist. New 
Jersey Agr. Exp. Sta. Ann. rept. i4:36?-377> fig. 35~4i- 

Symptoms of black rot well described (p. 374 _ 375)- Author makes the point that the 
fungus probably gains access through remnants of the flower at the free end. 

Harrison, Charles 

1823 A treatise on the culture and management of fruit trees, p. 1-356. 
Illustrated. 

Attributes (p. 341-343) canker to such causes as injudicious pruning, bruising, nailing, 
bad subsoil. Surgical methods recommended. 

Hartig, R. 

1894 Text-book of the diseases of trees, p. 1-33 1 . (Translated by Somer- 
ville and Ward.) 

Hartley, C. P. 

1908 a Some apple leaf-spot fungi. Science n. s. 27: 212. 

Reports the finding of eighteen different species of fungi on apple leaf spots in West 
Virginia, Sphaeropsis Malorum being among the common ones. 

1908b Some apple leaf-spot fungi. Science n. s. 28:157-159. 

Gives brief historical review of the question of the etiology of apple leaf spot. A list 
of several species of fungi found on spotted leaves is given, and inoculation experi- 
ments with certain of these are reported. Results indicate that Coniothyrium pirina 
is a wound parasite, while Coryneum fotiicolum appeared to be even less parasitic. 

1913 Twig canker on black birch. Phytopath. 3:248-249. 

Reports the isolation of a Sphaeropsis, closely resembling S. Malorum but with 
somewhat smaller spores, from swollen cankered black birch twigs {Betula lento. L.). 
Inoculation experiments show that the organism is parasitic only under certain 
conditions, nor is it regarded as the cause of the swollen cankers. 

Heald, F. D. 

1906 The black-rot o' apples due to Sclerotinia fructigena. Nebraska 
Agr. Exp. Sta. Ann. rept. 19:82-91. Illustrated. (See also 
p. 22, 61.) 

Points out that the term black rot is a confused one, having been used for diseases caused 
by both Monilia and Sphaeropsis. The two diseases are compared and contrasted 
as to symptoms. 

Hedges, Florence, and Tenny, L. S. 

1912 A knot of citrus trees caused by Sphaeropsis tumefaciens. U. S. 
Plant Indus. Bur. Bui. 247 : 1-74. Illustrated. 

Hesler, L. R. 

191 2 The New York apple tree canker. Indiana Acad. Sci. Proc. 
1911:325-339, fig. 1-7. 

Gives data concerning the geographical distribution, importance, symptoms, etiology, 
and control of the disease. The synonymy of the fungus is reviewed. 



136 Bulletin 379 

1913 Physalospora Cydoniae. Phytopath. 3: 290-295. Illustrated. 

Proves experimentally the genetic connection between Physalospora Cydoniae and Sphae- 
ropsis Malorum. 

1914 Biological strains of Sphaeropsis Malorum. Phytopath. 4:45. 

Results of cross-inoculation work with the fungus from several host plants indicate that 
there is one large morphological species embracing many biological races. 

Hewitt, J. L., and Hayhurst, P. 

191 1 Diseases of apple trees and fruit caused by fungi and insects. 

Arkansas Agr. Exp. Sta. Bui. 109:409-445. 

Note the occurrence of black rot and leaf spot in Arkansas (p. 438, 440-441). 

Howitt, I. E. 

1913 Fungus diseases. Ontario Agr. Coll. and Exp. Farm. Ann. 
rept. 38:29-30. 

Notes the occurrence of black rot canker along with other plant diseases . 

Ingram, Delia 

1912 Preliminary notes on a twig blight of Quercus prinus. Phyto- 

path. 2: 96-97. 

Mentions an apparently serious disease of the chestnut oak which occurs in Connecticut, 
Virginia, Maryland, and Pennsylvania. The organism associated with the disease is 
said to agree with Dothiorella quercina (C. & Ell.). (Cf. Rankin, W. H., 1914, p. 141.) 

Jehle, R. A. 

1913 The brown rot canker of the peach. Phytopath. 3:105-110, 

pi. 10, fig. 1-5. 

Reports successful use of coal tar on wounds of peaches. 

Jones, L. R., and Giddings, N. J. 

1907 Apple canker. In The occurrence of plant diseases in Vermont 
in 1906. Vermont Agr. Exp. Sta. Ann. rept. 19:231-232. 

The fungus Sphaeropsis Malorum said to continue its destructive invasion and to be the 
cause of every case of apple canker examined. 

Kern, F. D. 

1906 Indiana plant diseases in 1905. Purdue Univ. Agr. Exp. Sta. 

Bui. 111: 121-134. 

Black rot of the apple, pear, and quince reported (p. 125) from the southern part of the 
State only. 

1907 Indiana plant diseases in 1906. Purdue Univ. Agr. Exp. Sta. 

Bui. 119:425-436. 

Mentions (p. 428) black rot and canker of the apple, and black rot of quince, present 
to some extent in the southern part of the State. 

Kinney, L. F. 

1895 a Some special orchard treatment of the apple, pear, and quince. 
Rhode Island Agr. Exp. Sta. Bui. 31: 1-17, fig. 1-9. 

Reports (p. 10) failure to control black rot of quince by spraying. 

1895 b The leaf spot of the apple and pear. In Horticultural Division. 
Rhode Island Agr. Exp. Sta. Ann. rept. 7: 188-189, %• 7~ 8 - 

Points out resemblance of injury by apple leaf miner (.Tischeria malifoliella Clemens) 
to apple leaf spot. Spots on the leaves, r.nd spores of Phyllosticla pirina, which 
is regarded as the cause, are figured. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 137 

1895 c The brown rot. In Horticultural Division. Rhode Island 
Agr. Exp. Sta. Ann. rept. 7:192-193, fig. 12. 

Symptoms are given. The disease on the fruit (which author calls brown rot) 
and spores of the fungus are figured. 

Kirchner, Oskar 

1906 Die Krankheiten und Beschadigungen tmserer landwirtschaft- 
lichen Kulturpflanzen, p. 1-647. 

States (p. 440) that the canker disease of apple trees, caused by Diplodia pseudodi plodia 
limm., occurs in North America, France, and perhaps Germany. 

Lamson, H. H. 

1897 Department of Bacteriology. In Ninth annual report. New 
Hampshire Coll. Agr. Exp. Sta. Bui. 48:146-147. 

Bordeaux mixture said to have had little effect in controlling leaf spot due to Phyllosticta 
pinna; hence work was directed toward its control. 

1899 Apple diseases. In Notes on apple and potato diseases. New 
Hampshire Coll. Agr. Exp. Sta. Bui. 65:106-107, fig. 38-39. 

Notes the serious nature of leaf spot, which is said to be caused partly at least by 

Phyllosticta pirina. 

1901 Apple tree canker. In Thirteenth annual report. New Hamp- 

shire Coll. Agr. Exp. Sta. Bui. 87: 130. 

Reports the presence of a canker which is believed to be caused by a fungus. 

1902 The cold storage of apples. — Part II. Influence of cold storage 

on the decay of apples. Effect of wrapping apples in paper. 
New Hampshire Coll. Agr. Exp. Sta. Bui. 93:75-81, fig. 1. 

Sphaeropsis Malorum listed (p. 75) as one of three fungi which cause most of the rotting. 
Author concludes (p. 81) that a temperature of 34 F. is more effective than 40 to 
45° F., and that wrapping the fruit is of decided advantage in extending the keeping 
period beyond the first of June. Clean newspaper said (p. 81) to be just as effective 
as more expensive paper. 

1903 Leaf spot. In Fungous diseases and spraying. New Hampshire 

Coll. Agr. Exp. Sta. Bui. 101:61-62. Illustrated. 

Bordeaux mixture said to have little effect in controlling leaf spot of apple. 

Lewis, C. E. 

1909 Apple diseases caused by Coryneum foliicolum and Phoma 
Mali. Maine Agr. Exp. Sta. Bui. 170:183-200, fig. 17-42. 

Reports successful infection experiments with Sphaeropsis Malorum Peck on injured bark 
and on uninjured apple leaves. 

1912 Inoculation experiments with fungi associated with apple leaf 
spot and canker. Phytopath. 2:49-62. 

An account of experiments directed toward the determination of the parasitism of 
such fungi as Sphaeropsis Malorum, Phyllosticta limitala Peck, Coniothyrium pinna 
(Sacc.) Sheldon, and Coryneum foliicolum Fckl. Author concludes that a part of 
the leaf spot in Maine is due to Sphaeropsis Malorum, but that a similar spotting 
is due to bordeaux mixture; that Sphaeropsis Malorum is the only fungus isolated 
from apple leaves in the State which causes spots when inoculations are made from 
pure cultures; and that, of the several fungi studied, this fungus does the greatest 
damage to branches and to twigs. 

Lewis, I. M. 

1908 Apple leaf spot. New Hampshire Agr. Exp. Sta. Ann. rept. 
19-20:365-369, pi. 8-9. 

Gives a historical review of the causal nature of the disease, and presents inoculation 
and control data. 



138 Bulletin 379 

Lochhead, William 

1905 Black rot canker. Ontario Agr. Coll. and Exp. Farm. Ann. 
rept. 30:49, fig. 4-5. 

Defines the term canker and outlines control measures. 

1909 Apple diseases. In Fungous diseases in Quebec in 1908. Quebec 
Soc. Prot. Plants from Ins. and Fung. Dis. Ann. rept. 1:31. 

The prevalence of the canker form of this disease is noted. 

Longyear, B. O. 

1904 Fungous diseases of fruits in Michigan. Michigan State Agr. 
Coll. Exp. Sta. Spec. bul. 25:1-68, fig. 1-42. 

Records the black rot disease of apple (p. 10-13), pear (p. 16), and quince (p. 20). 

Lunge, George 

1909 Coal tar and ammonia, Part I, chap, i, p. 1-15. 

Notes differences in tars, both physical and chemical, depending on the origin. Tar 
obtained from the same material also differs very much in composition, according to 
the temperature of the dry distillation, and even according to the shape of the retorts. 

McAlpine, D. 

1902 Fungus diseases of stone-fruit trees in Australia and their treat- 
ment, p. 1-165. Illustrated. 

Lists (p. 133, 134) Diplodia Malorum on peach and plum twigs. 

M'Cormack, Edna F. 

1910 Black rot of the apple. In Fungous diseases of the apple. 

Indiana State Entomologist. Rept. 3:142-144. Illustrated. 

Symptoms discussed. 

McCready, S. B, 

19 10 Black rot canker (Sphaeropsis Malorum Peck). Ontario Agr. 

Coll. and Exp. Farm. Ann. rept. 35:41-42. 

Brief reference to hosts, distribution, etiology, and control. 

191 1 Black rot of apple. Ontario Agr. Coll. and Exp. Farm. Ann. 

rept. 36:37- 

Reports use of lead paint and gas tar as wound dressings; the latter found to give 
better protection. 

Mangin, L. 

1901 Sur une nouvelle maladie des pommiers causee par le " Diplodia 
pseudo-diplodia." Journ. agr. prat. n. s. 2:138-139. 

Reports occurrence of the disease on apple branches in France, and gives suggestions 
for control. 

Morse, W. J. 

1909 Notes on plant diseases, 190S. Maine Agr. Exp. Sta. Bul. 
164: 1-28. Illustrated. 

States (p. 3-4) that Sphaeropsis Malorum from leaf spot produced decay of fruit as a 
result of artificial inoculation. States (p. 10) that self-boiled lime-sulfur seemed 
effective in controlling leaf spot. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 139 

Morse, W. J., and Lewis, C. E. 

1910 Maine apple diseases. Maine Agr. Exp. Sta. 601.185:335-392. 
Illustrated. 

Notes on the etiology of leaf spot and canker. Canker fungus in Maine orchards follows 
frost injury. 

Munson, W. M. 

1909 Apple enemies, and how to fight them. West Virginia Univ. 
Agr. Exp. Sta. Bid. 121:353-366. 

Control measures for leaf spot and canker given (p. 360-362). 

Norton, J. B. S., and Symons, T. B. 

1907 Black-rot (Sphaeropsis Malorum). In Control of insect pests and 
diseases of Maryland crops. Maryland Agr. Exp. Sta. Bui. 
115:178. 

Give brief recommendations for the control of black rot, leaf spot, and canker. 

O'Gara, P. J. 

1902 Notes on canker and black-rot. Science n. s. 16:434-435. 

Notes a case of girdling of branches of sumac (Rhus glabra L.) by Sphaeropsis rhoina 
(Schw.) Starb., which fungus, after careful cultural and inoculation experiments, is 
regarded as probably identical with Sphaeropsis Malorum. 

Orton, C. R. 

1914 Black rot. /// Some orchard diseases and their treatment. 
Pennsylvania State Hort. Assoc. Proc. 55: 43-56. Illustrated. 

Author states that Sphaeropsis Malorum rarely if ever produces cankers on its own 
initiative. He notes its wide occurrence on various plants, and says that a perfect 
stage has recently been found on apple, quince, oak, grape, witch-hazel, and other 

hosts. 

Orton, W. A. 

1902-1907 Plant diseases in the United States in 1901-1907. U. S. 
Agr. Dept. Yearbook 1901:669; 1902:715; 1903:550; 
1904:582-583; 1905:603-604; 1906:499-500; 1907:577- 
579- 

Gives notes on the occurrence and destructiveness of black rot, leaf spot, 
and canker of apple, pear, and quince. 

Paddock, Wendell 

1898 a An apple canker. Science n. s. 8:595-596. 

Reports preliminary experiments in canker investigation. Cultures of fungi from 
cankers showed Schizophyllutn commune, and a dark-spored fungus which is said 
to resemble Sphaeropsis Malorum Peck. 

1898 b Additional notes on an apple canker. Science n. s. 8: 836-837. 

Suggests that Sphaeropsis Malorum Peck is parasitic on the wood of pear and quince 
as well as on that of apple. Cross-inoculations of the fruits of these three plants 
gave positive results. 

1899 a An apple canker. Western New York Hort. Soc. Proc. 44: 

58-63. Illustrated. 

(See 1899 b, of which this is a popular presentation.) 

1899 b The New York apple-tree canker. New York (Geneva) 
Agr. Exp. Sta. Bui. 163:177-206, pi. 1-6. 

Contains an account of host relationships, names of the disease, symptoms, etiology, 
and control. Presents conclusive data proving that Sphaeropsis Malorum is 
the cause of canker on apple; considerable data indicate that this species of 
Sphaeropsis also occurs on many other plants. 



140 Bulletin 379 

1900 The New York apple-tree canker (Second report). New York 
(Geneva) Agr. Exp. Sta. Bui. 185:203-213, pi. 1-4. 

States that Sphaeropsis Malorum occurs on apple, pear, and quince fruits, and on apple, 
pear, and hawthorn trees; and that it probably occurs on several other plants, but 
experiments are not regarded as warranting this as a definite conclusion. Notes that 
apple leaves are occasionally attacked by a Sphaeropsis. 

Parkinson, John 

1629 Paradisi in sole paradisus terrestris, p. 1-612. Illustrated. 

Briefly outlines (p. 550) the nature and control of canker. Of historical importance. 

Parrot, P. J., and Fulton, B. B. 

1913 Notes on tree crickets. Journ. econ. ent. 6: 177-180. Illustrated. 

Note that the penetration of apple bark tissues by the ovipositor of the tree cricket 
is apparently attended by an infection of some unknown fungus or bacterium, which 
results in the formation of a canker indistinguishable in its appearance and effects 
from the New York apple tree canker or the fire blight canker. 

1914 Tree crickets injurious to orchard and garden fruits. New York 

(Geneva) Agr. Exp. Sta. Bui. 388:415-461. Illustrated. 

Authors note (p. 442) that injuries by tree crickets are followed by some infectious agent, 
and that these lesions, in their external appearances and their effects, resemble super- 
ficially certain stages of the New York apple tree canker caused by Sphaeropsis 
Malorum. 

Peck, C. H. 

1879 Report of the Botanist. New York State Mus. Nat. Hist. 
Ann. rept. 31: 19-60. 

Reports (p. 20-21) the discovery of Sphaeropsis Malorum on apple fruits in Schoharie 
County. 

1881 Report of the Botanist. New York State Mus. Nat. Hist. 
Ann. rept. 34:24-58, pi. 1-4. 

Describes (p. 36) symptoms of black rot, and points out the fact that the distinction 
between Sphaeropsis and Diplodia sometimes fails, since both one- and two-celled 
spores are found in the same spore case. 

Pollock, J. B., and Kauffman, C. H. 

1905 Michigan fungi. Michigan Acad. Sci. Rept. 7: 57-67. 

List Sphaeropsis Mali (West.) Sacc. and 5. Malorum Peck. 

Potebnra, A. 

1907 Mycologische Studien. Ann. myc. 5: 1-28, pi. 1-3, fig. 1-43. 

Discusses mycelial development, including spore germination and protoplasmic 
streaming. 

1910 Beitrage zur Micromycetenflora Mittel-Ruszlands. Ann. myc. 
8:42-93, fig. 1-38. 

States that the pyenidia of 5. pseudodiplodia (Fckl.) Del. arise meristogenetically. 

1912 Pilzliche Symbionten. 2. Sphaeropsis und Helicomyces, p. 28. 
Illustrated. (Separate sent by Potebnia to the writer.) 

Price, H. L. 

1909 Black rot. In Fighting the insect pests and diseases of orchard, 
field, and garden crops. Virginia Agr. Exp. Sta. Circ. 
7 : 10-1 1, fig. 2. 

Recommendations for the control of black rot, leaf spot, and canker. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 141 

Quaintance, A. L., and Scott, W. M. 

1912 Apple leaf-spot. In The more important insect and fungous 
enemies of the fruit and foliage of the apple. U. S. Agr. 
Dept. Farmers' bul. 492:35-36, fig. 20. 

Discuss the importance, symptoms, etiology, and control of apple leaf spot caused by 
Sphaeropsis Malorum. 

Rankin, W. H. 

1914 Sphaeropsis canker of Quercus prinus. Phytopath. 4: 44-45. 

Reports Sphaeropsis Malorum Berk, as causing twig and limb cankers on chestnut nak 
{Quercus remits L.), the account being based on observation and inoculation experi- 
ments. Regards the disease as the one described by Miss Delia Ingram in 
Phytopathology 2:96 (p. E36). 

Reddick, Donald 

1912 Frost injury. New York State Fruit Growers' Assoc. Proc. 
11:34-41, fig. 1-2. 

Sphaeropsis Malorum said to be usually found following frost injury. 

Reed, H. S. 

1908 Fall blossoming of the apple induced by the black rot. Plant 
world 11: 256-257. 

Notes a case in which Sphaeropsis Malorum inhibited the normal activities of an apple 
tree, allowing the tissues to carry on the growth which would normally have been 
deferred for several months, and resulting in the unfolding of normal blossoms on 
October 5. 

Reed, H. S., and Cooley, J. S. 

191 1 Black rot (Sphaeropsis Malorum). In Plant diseases in Virginia 

in the years 1909 and 1910. Virginia (Polytech. Inst.) Agr. 
Exp. Sta. Ann. rept. 1909-1910: 102-103, fig- 2I - 

Record black rot. leaf spot, and canker. Report pyenospores discharging from pyenidia 
on leaves at Blacksburg on June 25, 1910. 

Reed, H. S., Cooley, J. S., and Rogers, J. T. 

1912 Foliage diseases of the apple. Virginia (Polytech. Inst.) Agr. 

Exp. Sta. Bul. 195:1-24, fig. 1-13. 

Give points concerning the varietal susceptibility of apples; the distribution, importance, 
and symptoms of the disease; and the life history of the fungus. 

Reed, H. S., and Crabill, C. H. 

1913 Black rot (Sphaeropsis Malorum). In Plant diseases in Virginia 

in the years 1911 and 1912. Virginia (Polytech. Inst.) Agr. 
Exp. Sta. Ann. rept. 1911-1912:36, fig. 3. 

Note that Sphaeropsis Malorum occurs on twigs previously killed by the fire blight 
organism. Figure a multilocular sterile (?) pyenidium. 

Reed, H. S., and Stahl, H. S. 

191 1 The erepsins of Glomerella rufomaculans and Sphaeropsis 
Malorum. Journ. biol. chem. 10:109-112. 

Authors find evidence of erepsin produced in pure cultures. 

Roberts, J. W. 

1913 The " rough-bark " disease of the Yellow Newtown app'e. 
U. S. Plant Indus. Bur. Bul. 280:1-15, pi. 1-3. 

Reports (p. 9, 15) Phomopsis Mali, a new species, associated with Sphaeropsis Malorum 
on leaf spots. 



142 • Bulletin 379 

1914 Experiments with apple leaf-spot fungi. Journ. agr. research 
2:57-66, pi. 7, fig. 1-3. 

Reports the isolation of several species, including Sphaeropsis Malorum, from apple Icf 
spots. A new species, Altcrnaria Mali, is in the list and is technically described. 
From experiments conducted it is concluded that this species may be classed as a 
rather strong facultative parasite. 

Rose, D. H. 

1914 Ring rot. Also, Black rot (Sphaeropsis Malorum). In Biennial 
report. Missouri State Fruit Exp. Sta. Bui. 24 (Bienn. rept. 
1913-1914)20, 23-24, pi. 5, fig. 1-2. 

Ring rot. or blossom-end rot, of the apple fruit thought to be due to frost injury at 
blossoming time, followed by Sphaeropsis Malorum Peck. Author gives notes on the 
destructiveness of black rot. 

Ruggles, A. G., and Stakman, E. C. 

191 1 Black rot In Orchard and garden spraying. Minnesota Univ. 

Agr. Exp. Sta. Bui. 121:15. 

Symptoms of black rot given. 

Saccardo, P. A. 

1884 a Phoma Malorum (Berk.) Sacc. Syll. Fung. 3:152-153. 

A technical Latin description is given. Author lists Sphaeropsis Malorum Berk, in 
synonymy. 

1884 b Sphaeropsis Malorum Peck. Syll. Fung. 3:294. 

Describes the fungus which Peck (1881) reports and regards as new, thus giving 
rise to the name Sphaeropsis Malorum Peck. 

Salmon, E. S. 

1907 Apple leaf-spots. Gard. chron. ser. 3:42:305-306, fig. 120-124. 

A brief discussion of varietal susceptibility and etiology of leaf spots caused by a species 
of Phyllosticta and one of Sphaeropsis. The author is in doubt as to whether the 
latter species is S. Malorum. 

Scott, W. M. 

1906 The control of apple bitter-rot. U. S. Plant Indus. Bur. Bui. 

93 :i ~36, pi. 1-8. 

Gives (p. 27-33) results of experiments for the control of leaf spot in connection with 
apple scab, sooty blotch, and bitter rot. 

1908 Apple leaf-spot. In Self-boiled lime-sulphur mixture as a 

promising fungicide. U. S. Plant Indus. Bur. Circ. 1:12. 

States that it appears that leaf spot may be prevented by this fungicide, but no data 
are cited. 

1912 Apple leaf -spot, or frog-eye. In Spraying to control the important 

insects and fungous diseases affecting the fruit and foliage of 
the apple. Thomsen Chemical Co. (Baltimore, Md.). Circ. 

4:14-15, pi. 2, fig. 1. 

Scott, W. M., and Quaintance, A. L. 

1907 Leaf-spot diseases. In Spraying for apple diseases and the 

codling moth in the Ozarks. U. S. Agr. Dept. Farmers' bid. 
283:18-20, fig. 3. 

Authors give recommendations for the control of leaf spot, which, as they state, mav 
be due to Sphaeropsis Malorum. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 143 

Scott, W. M., and Rorer, J. B. 

1908 Apple leaf-spot caused by Sphaeropsis Malorum. U. S. Plant 

Indus. Bur. Bui. 121:45-54, pi. 3-4. 

Authors discuss the common names of the leaf spot, its history, geographical occur- 
rence, importance, symptoms, etiology, and control. Proof of the pathogenicity of 
Sphaeropsis Malorum on apple leaves is given, together with a study of the role of 
associated fungi on leaf spots. 

1909 Apple blotch, a serious disease of Southern orchards. U. S. 

Plant Indus. Bur. Bui. 144:1-28, pi. 1-6. 

Authors suggest (p. II) that Sphaeropsis Malorum is a factor in the killing of apple buds 
Further investigation is deemed desirable. 

Scribner, F. L. 

1890 Black-rot of the apple. Fungus diseases of the grape and other 
plants and their treatment, p. 81-83, fig- 1606. 

Descriptions of the disease and of the fungus, called Macrophoma Malorum, are given. 

Seaver, F. J. 

1908 Color variation in some of the fungi. Bui. Torrey Bot. Club 
35:307-3i4- 

Points out that color characters are misleading and misused in the Hypocreales. 

Selby, A. D. 

1900 A condensed handbook of the diseases of cultivated plants in 
Ohio. Ohio Agr. Exp. Sta. Bui. 121:1-69, fig- I_ 54- 

Notes (p. 14) the disease on the leaves and fruit of apple and quince. 

1910 Black-rot. In A brief handbook of the diseases of cultivated 

plants in Ohio. Ohio Agr. Exp. Sta. Bui. 214:368-369, 
436, fig. 1-105. 

Notes the importance of the disease in Ohio. 

1913 Disease susceptibility of apple varieties in Ohio. Ohio Agr. Exp. 
Sta. Circ. 133:53-56- 

Indicates degree of susceptibility of apple varieties to black rot and canker. 

Shear, C. L. 

1910 Life history of Melanops Quercuum (Schw.) Rehm forma Vitis 
Sacc. Science n. s. 31: 748. 

Pure cultures of ascospores of Mela>mp^ Quercuum (Schw.) Rehm forma Vitis Sacc. 
[^ Bolryosphaeria Berengeriana de Not. == B. fuliginosa (M. & N.J E. & E.] said to 
produce a pyenidial form which agrees with Sphaeropsis Malorum Berk, and Diplodia 
Pseudodiplodia Fckl. 

1913 Some observations on phytopathological problems in Europe and 

America. Phytopath. 3:77-87. 

Sphaeropsis Malorum reported (p. 81-82) as doing no noticeable injury in orchards 
from Italy to England. 

1914 Life history of Sphaeropsis Malorum Berk. Phytopath. 4: 4S-49. 

Concludes from cultural studies the ascosporic form of Sphaeropsis Malorum Berk. 
is Melanops Quercuum f. Vitis. 

Shear, C. L., and Wood, Anna K. 

1913 Studies of fungous parasites belonging to the genus Glomerella. 
U. S. Plant Indus. Bur. Bui. 252:1-110. Illustrated. 

Discuss host relationships, variability, and parasitism of Glomerella. 



144 Bulletin 379 

Sheldon, J. L. 

1905 A report on plant diseases of the State. West Virginia Univ. 
Agr. Exp. Sta. Bui. 96:69-99. Illustrated. 

Black rot (p. 74). leaf spot (p. 74-75), and canker (p. 74) reported. 

1907 The taxonomy of a leaf-spot fungus of the apple and other 

fruit-trees. Torreya 7: 142-143. 

The name of the leaf spot, or frog-eye, organism is changed from Phyllosticta pirina Sacc. 
to Coniothyrium pirina (Sacc.) Sheldon. 

1908 Another leaf-spot fungus of the apple. Torreya 8: 139-141. 

IUosporium malifoliorum n. sp. is said to be concerned with the leaf spot, in a secondary 
manner. This fungus is described. 

Smith, R. I., and Stevens, F. L. 

1910 Leaf spot. Also, Black rot. In Insects and fungous diseases of 
apple and pear. North Carolina Agr. Exp. Sta. Bui. 206: 
94, 95. 102-103, %• 2 3- 

Call the disease Sphaeropsose, and state that perhaps one, but probably several, species 
are responsible for leaf spot. 

Stene, A. E. 

1910 Some suggestions for Rhode Island apple growers. Rhode 
Island State Agr. Bd. Ann. rept. 25:93-181. Illustrated. 

Leaf spots and canker said to be general in the State (p. 152-153). 

Stevens, F. L., and Hall, J. G. 

1907 Sphaeropsis on apple twigs. In Some apple diseases. North 
Carolina Agr. Exp. Sta. Bui. 196:52-53. 

1909 a Notes on plant diseases occurring in North Carolina. North 

Carolina Agr. Exp. Sta. Ann. rept. 31:66-82, fig. 1-10. 

Black rot and canker reported (p. 66). Sphaeropsis and an ascomycetous fungus 
found; name of latter not given. Sphaeropsis reported (p. 75) as a canker-pro- 
ducing fungus on pear. 

1909 b Variation of fungi due to environment. Bot. gaz. 48: 1-30, 
fig- I_ 37- $ ee a ^ s P North Carolina Agr. Exp. Sta. Ann. 
rept. 32 (1908-1909): 47-71, rig. 1-37. 

Authors discuss observations on the influence of environment on the characters of 
certain fungi. 

Stevens, F. L., and Sherman, F. 

1903 The black rot. Also, The black rot of the quince. In Insect 
arid fungus enemies of the apple, pear, and quince, with methods 
of treatment. North Carolina Agr. Exp. Sta. Bui. 183:72, 
82, fig. 1-22. 

Symptoms and control measures of black rot and canker given. 

Stewart, F. C. 

1896 A new leaf -spot disease of apples. In Report of the Mycologist. 
New York (Geneva) Agr. Exp. Sta. Ann. rept. 14 (1895): 
S4S-546. 

Records Phyllosticta limttata n. sp. on apple leaves on Long Island. Technical descrip- 
tion given. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 145 

1904 Apple canker. In Fungi and fungous diseases. Western New 
York Hort. Soc. Proc. 49: 53. 

States that spraying for apple canker caused by Sphaeropsis M alarum is only a partial 
preventive; a matter not understood. 

1909 Apple leaf spot. In Recent investigations on plant diseases. 

Western New York Hort. Soc. Proc. 54: 78-79. 

Believes that the leaf spot problem in New York is not completely solved. Points out 
that spraying often fails to control. 

1910 Notes on New York plant diseases, I. New York (Geneva) Agr. 

Exp. Sta. Bui. 328:303-404, pi. 1-18. 

Discusses (p. 312-313) occurrence of leaf spot in New York. Gives (p. 323-324) an 
account of a peculiar disease of the trunk of Walbridge apples and suggests that 
Sphaeropsis Malorum may have been a factor in producing the same. Suspects (p. 377- 
379) that the fungus also causes the failure of grafts of the pear. 

Stewart, F. C, and Blodgett, F. H. 

1899 A fruit-disease survey of the Hudson Valley in 1899. New York 

(Geneva) Agr. Exp. Sta. Bui. 167:273-308, pi. 1-4. 

Notes on the geographical occurrence of the leaf spot and canker in the Hudson Valley 
(p. 283. 284. 301-302). 

Stewart, F. C, and Eustace, H. J. 

1902 Two unusual troubles of apple foliage. New York (Geneva) 

Agr. Exp. Sta. Bui. 220:215-233, pi. 1-5. 

Authors conclude that spray material caused spotting of apple foliage; suspect the 
parasitism of Phyllosticta; suggest that drops of rain may act as lenses and concen- 
trate the sun's rays, overheating the tissue beneath. 

Stewart, F. C, Rolfs, F. M., and Hall, F. H. 

1900 A fruit-disease survey of western New York in 1900. New York 

(Geneva) Agr. Exp. Sta. Bui. 191:289-331, pi. 1-6. 

Note geographical occurrence of the disease in western New York. 

Stone, G. E. 

1914 Lime and sulfur solutions. Massachusetts Agr. Exp. Sta. 
Circ. 39:1-4- 

Lime and sulfur said to hold leaf spot in check, and believed to have material effect on 
cankers. 

Stone, G. E., and Fernald, H. T. 

1908 Canker. In Fungicides, insecticides, and spraying directions. 
Massachusetts Agr. Exp. Sta. Bui. 123:16. 

Suggestions for canker control are given. 

Stone, G. E., and Monahan, N. F. 

1907 The lime and sulfur mixture as a fungicide. In Report of the 
Botanist. Massachusetts (Hatch) Agr. Exp. Sta. Ann. rept. 
19: 167. 

State that observations seem to indicate that spraying with lime and sulfur succeeds to 
some extent in controlling canker. 

Stone, G. E., and Smith, R. E. 

1903 Apple-leaf spot. In Report of the Botanists. Massachusetts 

(Hatch) Agr. Exp. Sta. Ann. rept. 15:27, 32-34. 

Frost followed by cold wet weather caused apple leaf spot. 



146 Bulletin 379 

Sturgis, W. C. 

1893 a Black-rot (Sphaeropsis Malorum Peck). In Common fungous 
diseases and their treatment. Connecticut (New Haven) 
Agr. Exp. Sta. Bui. 115:6-7. 

Black rot of apple, quince, and pear noted. 

1893 b Black rot of quinces. In Report of the Mycologist. Con- 

necticut (New Haven) Agr. Exp. Sta. Ann. rept. 1892 : 43-44. 

Description of black rot disease of quince fruits. 

1894 Black rot (Sphaeropsis Malorum Peck). In Report of the 

Mycologist. Connecticut (New Haven) Agr. Exp. Sta. 
Ann. rept. 17:78-79. 

Reports inoculation and spore germination data. States that the wind and other 
agencies carry the fungus spores. 

Taft, L. R., and Davis, G. C. 

1895 Black rot (Sphaeropsis Malorum Berk.). In The pests of the 

orchard and garden. Michigan State Agr. Coll. Exp. Sta. 
Bui. 121:21. 

Briefly describe black rot and give suggestions for control. 

Taubenhaus, J. J. 

1912 A further study of some Gloeosporiums and their relation to a 
sweet pea disease. Phytopath. 2: 153-160, pi. 16, fig. 1-19. 

States (p. 157) in a footnote that black rot was very prevalent in the very dry summer 
of 191 1. 

Taylor, W. A. 

1914 Fruit diseases. In Report of the Chief of the Bureau of Plant 
Industry. U. S. Agr. Dept. Rept. 1913: 105-133. 

States (p. 107) that a variety of Melanops Quercuum has been shown to be the perfect 
stage of Sphaeropsis Malorum. 

Thiimen, F. von 

1879 Fungi pomicoli, p. 10S. (Cited from Baccarini, 1S90.) 

Waite, M. B. 

1898 a An apple canker. Western New York Hort. Soc. Proc. 
43:9-11- 

Briefly outlines the history and distribution of the disease, and suggests that the 
cause may be Schizophyllum commune. Control measures suggested. 

1898 b An apple canker. Rural New-Yorker 57:82, fig. 32. 

Essentially the same paper as the preceding. 

1906 Fungicides and their use in preventing diseases of fruits. U. S. 
Agr. Dept. Farmers' bul. 243:1-32, fig. 1-17. 

Brief notes (p. 19) on control of black rot, leaf spot, and canker. 

1908 Apple leaf blight. In Diseases of orchard trees and fruits. 
Pennsylvania Agr. Dept. Ann. rept. 13:450-452. 

Gives treatment for leaf spot. 

1910 Experiments on the apple with some new and little-known 
fungicides. U. S. Plant Indus. Bur. Circ. 58:1-19. 

Notes on leaf spot. 



Black Rot, Leaf Spot, and Canker of Pomaceous Fruits 147 

Walker, Leva B. 

1908 A new form of Sphaeropsis on apples. Nebraska Agr. Exp. 
Sta. Ann. rept. 21 : 34-44, fig. 1-10. 

Compares typical Sphaeropsis Malorum with a new form, the latter having larger 
spores, pycnidia with long necks, and no ostiole, and being more virulent in producing 
black rot. 

Wallace, Errett 

1913 Scab disease of apples. Cornell Univ. Agr. Exp. Sta. Bui. 
335 : 54 I ~624- Illustrated. 

Warren, G. F., and McCourt, W. E. 

1905 The apple-tree canker. In An apple orchard survey of Wayne 

County, New York. Cornell Univ. Agr. Exp. Sta. Bui. 
226:341-345, fig. 86-87. 

Attention is given to the economic importance of the canker and to control measures 
followed by the growers in this section of the country. It is said that very few mature 
Twenty Ounce trees are not badly cankered, and Esopus suffers seriously. 

Whetzel, H. H. 

1906 The blight canker of apple and pear trees. Western New York 

Hort. Soc. Proc. 51:36-45. 

Compares fire-blight and New York apple-tree cankers. 

1907 The New York apple tree canker. In Fighting the fungi in their 

winter quarters. Cornell reading-course for farmers, March, 
1907, p. 670-671, fig. 365. 

Gives symptoms of canker and measures for its control. 

Whetzel, H. H., and Stewart, F. C. 

1908 New York apple-tree canker. In Insect pests and plant diseases. 

IV. _The control of plant diseases Cornell Univ. Agr. Exp. 
Sta. Bui. 252:3-1, fig. 165. 

Suggestions for canker control are given. 

Wilcox, E. M. 

1905 Black rot. Also Canker. In Diseases of the apple, cherry, 
peach, pear, and plum; with methods of treatment. Alabama 
(Auburn) Agr. Exp. Sta. Bui. 132 : 89-93, pi- 2 > %• 6. 

Notes on symptoms and control of black rot and canker. 

Wilcox, E. M., and Stone, R. E. 

1909 Black rot (Sphaeropsis Malorum). hi Directions for the control 

of Nebraska plant diseases. Nebraska Agr. Exp. Sta. Ann. 
rept. 22:31. 

Give schedule for control of canker and black rot. 

Wilson, G. W. 

1913 New York canker. In Notes on three limb diseases of apple. 
North Carolina Agr. Exp. Sta. Ann. rept. 35:47-49, tig- r. 

Brief summary of history, distribution, importance, and symptoms of the disease. 
Author states that the fungus may enter the bark under certain conditions, and that it 
does not travel in the wood. 



148 Bulletin 379 

Wolf, F. A. 

1910 The prevalence of certain parasitic and saprophytic fungi in 
orchards as determined by plate cultures. Plant world 
13: 190-202. 

By use of trap cultures the author concludes that at no time during the period in which 
exposures were made {September to May) were viable spores of Sphaeropsis Malorum 
present in the atmosphere of the orchard. 

1913 Control of apple black-rot. Phytopath. 3:288-289. 

Suggests that apple mummies are a source of the inoculum. Reports that in the 
South lime-sulfur alone is effective against the disease; bordeaux 4-4-50 also 
satisfactory. A spraying schedule is given. 



